Digital Pressure Transmitter EDT 23

Transcription

1 Digital Pressure Transmitter EDT 23 User manual Rev. 14 August 2014

2 This document provides functional description, installation, configuration and operating instructions for ELGAS EDT 23 pressure transmitter with Modbus protocol. The information in this document covers software revision Information in this document is subject to change without notice and does not represent a commitment on the part of ELGAS, s.r.o. Improvements and/or changes in this manual or the product may be made at any time. These changes will be made periodically to correct technical inaccuracies or typographical errors.

3 Contents 1 Introduction Device overview Available versions Functional description Mechanical construction Device specification Installation Mechanical installation Electrical installation Cabling, grounding Power supply requirements Modbus communication Overview of Modbus conventions Physical communication layer Transactions on Modbus networks Device specific features Service address Communication buffer length Response time Holding registers map Overview of the holding registers map Factory configuration section Service configuration section User configuration section Miscellaneous Measured variables Datalogger section Data types Discrete outputs map Overview of the discrete outputs map Master reset Write EEPROM

4 4.4.4 Read EEPROM Stop measurement Start single measurement Start continuous measurement Unlock user configuration section Unlock service configuration section Change password Modbus function codes Read multiple registers (03h) Force single coil (05h) Write multiple registers (10h) Start measurement with mask (45h) Synchronize datalogging (46h) Erase data (47h) Set slave address (48h) Exception responses Related Publications

5 Abbreviations and terms char CRC dec EEPROM float FS hex int LSB Modbus MSB RS 485 RTU uchar uint 8-bit signed integer value Cyclical Redundancy Check Decimal representation Electrically erasable non-volatile memory 32-bit single precision floating point value Full scale Hexadecimal representation 16-bit signed integer value The least significant byte A vendor-neutral communication protocol intended for supervision and control of automation equipment. The most significant byte Standard for data transmission, where a balanced (differential) transmission line is used in a multidrop configuration. Remote terminal unit. One of two serial transmission modes of the Modbus communication protocol. 8-bit unsigned integer value 16-bit unsigned integer value 3

6 1 Introduction The EDT 23 digital pressure transmitter is a miniature precision device intended for pressure measurement in applications which require a high precision and ultra low power consumption. The transmitter has a direct digital output on RS 485 bus which makes it ideal for use in modern digital systems. The primary use of the EDT 23 pressure transmitter is as a pressure sensing device for data loggers, gas-volume correction devices and remote monitoring systems. Features Ranges kpa gage to kpa gage, kpa abs to kpa abs RS 485 digital output with Modbus protocol Ultra low power consumption 4 μa standby, 1 ma active, operates from 2.9V High precision ±0.1% FS or ±0.25% of reading Small size, rugged stainless steel housing Certified as explosion-proof with type of protection II 2G Ex ia IIC T4 Gb 2 Device overview 2.1 Available versions EDT 23 pressure transmitter is available in several versions according to the pressure fitting, electrical connection and explosion-proof design. If not otherwise noted, stated parameters are valid for all versions. If a parameter is specific for the particular version, a letter indicating the version is given. Electrical connection versions: Version A: ribbon cable PNLY Version B: M12 connector Version C: integral shielded cable Version D: DIN connector Explosion-proof versions: Version I: type of protection "i" - intrinsically safe device Version -: without explosion-proof design 2.2 Functional description Figure 1 shows a simplified functional diagram of the EDT 23 pressure transmitter. The pressure transmitter is based on a silicon piezoresistive sensor. The signal from the sensor is converted in a high resolution analog-to-digital converter and brought into a microcontroller 4

7 which digitally compensates for the non-linearity and temperature drift of the sensor. Calibration data are stored in non-volatile EEPROM memory. Pressure readout as well as all control functions are accessible via RS 485 interface. The transmitter is capable to measure the pressure on request or continuously in preset time intervals and store values in its internal memory for later retrieval. Figure 1. Simplified functional diagram of the EDT 23 pressure transmitter. 2.3 Mechanical construction Figure 2 illustrates an exploded view of the EDT 23 pressure transmitter in the standard version with ERMETO M12x1.5 pressure fitting and integral cable. Stainless steel encapsulated pressure sensor is welded into sensor housing with pressure fitting. Two printed circuit boards secured to the rear of the pressure sensor contain microcontroller and supporting components. A stainless steel case encloses the electronics and permits subsequent fitment of the cable gland or connector. Figure 3 shows a dimensional drawing of EDT 23 pressure transmitter according to the electrical connection version. 5

8 Figure 2. Exploded view of the EDT 23 pressure transmitter with integral shielded cable. 6

9 Version A Version C M Version B Version D Figure 3 Dimensional drawing of the EDT 23 pressure transmitter according to the electrical connection version. 7

10 2.4 Device specification Operating pressure range Standard ranges: Absolute pressure: 80 to 520 kpa, 200 to 1000 kpa, 400 to 2000 kpa, 700 to 3500 kpa, 1400 to 7000 kpa Gage pressure: 0 to 20 kpa, 0 to 100 kpa, 0 to 160 kpa, 0 to 400 kpa, 0 to 600 kpa, 0 to 1000 kpa, 0 to 2500 kpa, 0 to 4000 kpa, 0 to 7000 kpa Other ranges available within limits kpa to kpa gage and kpa to kpa absolute. Please contact the manufacturer. Pressure fitting Standard: ERMETO M12 x 1.5 Adapters available on request. For other pressure fitting please contact the manufacturer. Pressure media Fluids compatible with a fully welded assembly of 316 (1.4401) stainless steel. Maximal overpressure The nominal pressure can be exceeded by the following multiples without danger of mechanical destruction and without loss of the tightness: transmitter for absolute pressure: 15 MPa transmitter for gage pressure: 3x or max. 15 MPa (whichever is lower) Overpressure 1 The rated pressure can be exceeded by the following multiples without degrading performance: transmitter for absolute pressure: transmitter for gage pressure: Accuracy 1 1,25 x 2x ±0.25% of reading (absolute sensor, all ranges) ±0.1% FS (gage sensor, ranges 100 kpa and higher) ±0.3% FS (gage sensor, ranges below 100 kpa) Comprises non-linearity, hysteresis, repeatability and temperature effects within operating temperature limits. Long term stability 1 ±0.1% of reading for 12 months (absolute sensor) ±0.1% FS for 12 months (gage sensor), ranges 100 kpa and higher ±0.3% FS for 12 months (gage sensor), ranges below 100 kpa 8

11 Measurement time 2 Software selectable: from 30 ms for 12 bit resolution to 650 ms for 16 bit resolution. Electrical connection Version A: ribbon cable PNLY 4 x 0.15 Version B: M12 connector Version C: 1 meter integral shielded cable 4 x 0.25 mm 2 with outer diameter 5 to 7 mm supplied as standard. Longer lengths available on request. Cable shielding is not connected to the transmitter s case. For gage transmitters, a cable with a venting tube is used. Version D: DIN male connector Power supply External power supply required. The transmitter operates on terminal voltage of 2.9 to 10 V dc. Reverse polarity protected with parallel diode (IF = 200 ma). Power consumption Standby current: 4 μa typical / 10 μa maximum Operating current: 1 ma typical / 4 ma maximum (measurement and/or communication) Standby and operating current does not depend on power supply voltage. Operating current during communication is highly dependent on bus impedance. Turn-on time The transmitter is ready to operate 50 ms after power supply is applied. Digital interface RS 485, 2-wire half-duplex, minimum bus impedance 1.5 kω, unterminated bus recommended for low-power consumption. Wiring length max. 100 m. Communication protocol Modbus RTU, baud rate bit/s, 1 start bit, 8 data bits, no parity, 1 stop bit. Supported standard function codes 03h (read multiple registers), 05h (force single coil), 10h (write multiple registers) + proprietary function codes 45h, 46h, 47h, 48h. 9

12 Datalogging The transmitter is capable of automatic pressure measurement and of storage measured values into memory, wherefrom it can be read by control unit later on. Measurement period: Data memory: Precision of time base: selectable 50 ms to 512 s 80 values ±100 ppm Insulation Greater than 10 MΩ at 500 V AC, case and cable shielding versus signal and power-supply wires. Physical specifications Dimensions: see chapter 2.3. Weight: g (standard cable length) Environmental specification Operating temperature: -25 C to +60 C standard -25 C to +70 C optional -25 C to +85 C optional -40 C to +85 C optional Storage temperature: -40 C to +85 C Humidity: 0% to 95% relative humidity, non-condensing Sealing version A: IP 20 version B, C,D: IP 65 Vibration: 10g sinusoidal Hz, EN [8] Electro-magnetic compatibility Complies with EN [2] Electrostatic discharge immunity test, EN : 8 kv, criterion B Electrical fast transients/burst immunity test, EN : 2 kv, criterion B Radiated radio-frequency electromagnetic field immunity test, EN : MHz, 10 V/m, criterion A Surge impulse, EN : 1 kv, criterion B Immunity to conducted disturbances induced by radio-frequency fields, EN : MHz, 10 V/m, criterion A 10

13 Explosion-proof design Version I: A device with the type of protection i (intrinsically safe device) according to the standards EN [9] and EN [10]. The certificate is registered under number FTZÚ 01 ATEX 0083 by FTZÚ Ostrava-Radvanice in Czech Republic, EU notified body no Location: hazardous area Zone 1,2 according to the EN [11] Protection class: II 2G Ex ia IIC T4 Gb Safety descriptions: Ui = 10 V Ci = 1.7 μf Li = 0 μh Pi = 1.20 W for Ta<60 C Pi = 1.10 W for Ta<70 C Pi = 0.95 W for Ta<85 C Note 1 The parameters given in Overpressure, Accuracy and Long-term stability paragraphs are guaranteed by sensing element selection and manufacturing / test procedures and are considered as a standard option for 25 C to +60 C operating temperature range. Other parameter specifications are available on request, but it is necessary to consult them with the manufacturer. Please note that there is always compromise between overpressure ratio, operating temperature range, accuracy and long-term stability. Higher overpressure ratio usually results in reduced accuracy and/or stability and vice versa. Similarly, operating temperature limits can be extended however accuracy is reduced. 11

14 3 Installation 3.1 Mechanical installation Mount the transmitter close to the process and use a minimum of piping to achieve the best accuracy. Keep in mind, however, the need for easy access, safety of personnel, practical field calibration, and a suitable transmitter environment. In general, install the transmitter to minimize vibration, shock, and temperature fluctuations. For the gage transmitters with integral cable (version C), a cable with venting tube is used. This type of cable must not be bent with diameter less than 50 mm. For the gage transmitters with connectors (version B and D) the atmospheric pressure (reference pressure) has access to the sensor back side via the connector assembly which is never hermetically tight. Operating position of the transmitter is arbitrary. 3.2 Electrical installation Wires in the cable or the connector pins carry the following signals: Signal Description Version A Version B Version C Version D color Pin no. color Pin no. GND negative power rail (ground) green 3 green 2 PWR positive power rail yellow 1 brown 1 DATA- RS485 inverted data signal blue 4 yellow DATA+ RS485 non-inverted data signal white 2 white 3 Version B, connector M12 pin assignment (top view on the transmitter): Version D, connector DIN pin assignment (top view on the transmitter):

15 Recommended types of mate connectors are: Version B: Binder 713, type Version D: Hirschmann, type GDM seal GDM 3-16 To operate the transmitter, apply DC voltage 2.9 to 10 V across PWR and GND terminals and connect the DATA+, DATA- signals with the corresponding terminals on the host RS 485 port. The EDT 23 transmitter does not provide electrical isolation between the RS 485 bus and the transmitter power supply. Figure 7 shows a multidrop wiring topology. Up to 32 devices may be wired on one RS 485 bus. Each device on the bus must be assigned to a unique slave address. Figure 4. Multidrop topology. To achieve low power consumption, the transmitter uses a special RS 485 driver with limited slew rate. It is recommended to leave the RS 485 bus unterminated to maintain power consumption as low as possible. The bus impedance must not be lower than 1.5 kω. The length of the bus should not exceed 100 m. For longer wiring lengths, a signal distortion due to reflections can occur and communication reliability can be deteriorated. Any standard RS 485 driver / receiver can be used in the host, however for the low power applications with unterminated bus it is recommended to use a driver with a reduced slew-rate and a receiver with a high input impedance. Suitable types are MAX 3471 form Maxim Integrated Products or ADM 483E from Analog Devices. 1.1 Cabling, grounding The transmitter is being interconnected with the control unit using a shielded 4-wire cable with min. cross-section of the core 0.15mm 2. The cable should not be laid along power cables, lightning conductors and long metal objects, it should not pass through areas with strong electro-magnetic disturbances or discharges. The suitable cable type is Lappkabel, LiYCY 4x0.25 or equivalent. The recommended signal to color assignment is given in the following table. 13

16 Signal Description Color of conductors GND Minus power supply pole (earth) green PWR Plus power supply pole brown DATA- Inverted signal RS 485 yellow DATA+ Non-inverted signal RS 485 white The transmitter case, control unit enclosure and interconnecting cable shielding have to be grounded to ensure electrostatic charge dissipation. The cable shielding on the side of control unit should be connected with ground and with the control unit enclosure, if this is metallic. The transmitter is usually installed in such a way, that it is galvanically connected to a grounded structure (machinery, metal piping etc.) which is sufficient for electrostatic charge dissipation. In this case, the cable shielding remains unconnected on the side of the transmitter, not to introduce a ground loop, see Fig. 5. If the transmitter is installed in such a way that it is electrically isolated from any grounded structure (for instance by a plastic tube), additional connection to the ground potential is required. Transducer Host Fig. 5. Grounding the transmitter variant. 3.3 Power supply requirements The EDT 23 pressure transmitter is optimized for very low-power applications. It operates from unregulated single supply voltage from 2.9 V to 10 V. The power supply current is independent from the supply voltage. Power supply terminals are reverse polarity protected with diode connected between PWR and GND terminals as shown in Figure 6. Maximum continuos forward current of the protection diode is 200 ma, maximum peak forward current is 450 ma. 14

17 Figure 6. Reverse polarity protection The transmitter uses an advanced algorithm to maintain the power consumption at a minimum level. Only the modules of the transmitter which are necessary for the requested function are powered on, while the unused modules are switched off. Due to the power consumption management, the supply current changes significantly depending on the performed function. Figure 7 illustrates an example of the power supply current vs. time plot. First, a supply current waveform is shown, when a simple query is received, processed and responded by the transmitter RS 485. Next, a supply current waveform during pressure measurement is shown. Figure 7. Power supply current waveform. The following table summarizes transmitter s typical average supply current for various measurement periods. The values are given provided each measurement is initiated by the Start Measurement command and result is read by the Read Multiple Registers command. Measurement period [s] Average supply current [µa] 15

18 Continuous measurement 800 0, Standby 4 4 Modbus communication In order to assure a complete understanding of the operation of the device, the user should familiarize himself with the Modbus protocol [1]. The EDT 23 pressure transmitter is referred shortly as Transmitter in further text. Values are given in decimal representation by default. If hexadecimal representation is used, suffix h or hex is added. 4.1 Overview of Modbus conventions The transmitter is a Modbus compatible measurement device. The transmitter supports 8-bit Remote Terminal Unit (RTU) data transmission mode with a subset of read and write commands used by most Modbus compatible host controllers and a few proprietary commands Physical communication layer The communication parameters are set at 1 start bit, 8 data bits and no parity, 1 stop bit, baud rate bit/s. These parameters are not configurable Transactions on Modbus networks The Modbus protocol uses a master/slave technique, providing for one master and up to 247 slaves. Only the master can initiate a transaction. Transactions are either a query/response type where only a single slave is addressed, or a broadcast/no response type where all slaves are addressed. The host (master) controller can produce query frames or broadcast frames. Query frames generate a response frame from one slave device. Broadcast frames address all slave devices, but none of them responds. A query/response message includes one query frame and one response frame. A broadcast message includes one broadcast frame. In RTU mode, frames start with a silent interval of at least 3.5 character times. The first field then transmitted is the address field followed by a function field, a data field, and an error check field. Following the last transmitted character, a similar interval of at least 3.5 character times marks the end of the frame. A new frame can begin after this interval. The entire message frame must be transmitted as a continuous stream. If a silent interval of more than 1.5 character times occurs before completion of the frame, the receiving device flushes the incomplete message and assumes that the next byte will be the address field of a new message. 16

19 Format of query and response frame Start 3.5 char times Address field 1 char Function field 1 char Data field n chars CRC field 2 chars End 3.5 char times Address field In a query frame, the address field contains a slave address. In a response frame, the address field contains the address of the responding slave device. Valid slave addresses are in the range of decimal. Address 0 is reserved for broadcast messages. Any query message with a slave address of 0 is a broadcast message which all slave devices process but they do not generate any response. Function field In a query frame or a broadcast frame, the function field contains a function code, which indicates the command to be performed. In a response frame, the function field contains a function code verifying the device s response to the command. If the most significant bit in the function field is set, the data field contains an exception response that explains any errors encountered while processing the command. Data field The data field contains information that is specific to each individual function. Error check field The error check field contains a 16 bit CRC checksum that is used to verify the integrity of the message frame. 4.2 Device specific features Service address Due to the small dimensions of the transmitter, no DIP switches or similar components can be used for slave address setting. Instead, the slave address is software configurable. In some cases, however, the slave address can be unknown. Thus a service address 248 (dec) has been assigned which the transmitter always respond. Any query frame with a slave address of 248 (dec) the transmitter processes and generates a response. The response is returned with the actual slave address in the address field instead of the service address 248 (dec). When using the service address, only one transmitter may be connected on the bus Communication buffer length The transmitter implements communication buffer 64 bytes long. If the length of the query frame exceeds capacity of the buffer, the frame is flushed and no response is generated. If the 17

20 host requires such amount of data to be sent which exceeds the capacity of the buffer, the response is truncated to the total frame length of 64 bytes Response time The transmitter responds to a query after 2 30 ms depending on the length of the query and response. 4.3 Holding registers map The transmitter s memory is mapped into Modbus holding registers address space (4xxxx reference). This address space can be read by the Read multiple registers (03h) command and written by the Write multiple registers (10h) command. The commands are described in chapter 4.5. All registers are 16 bit long. Register numbers shown in the text are in the 4xxxx format which follows the Modicon protocol specification for data item addressing. The actual register address sent in the Modbus message frame is the register number shown in the text minus In other words, the leading "4" is omitted, and the remaining 4-digit number is decremented by Overview of the holding registers map The following table shows holding registers map of the transmitter. The individual registers are described in subsequent paragraphs. Section name Factory configuration Register no. Register name Data type Access control Stored in EEPROM Hardware revision number uint FP N Software revision number uint RO N Serial number ulong FP Y Sensor type uint FP Y not used FP Y Units uint FP Y Operation range lower limit float FP Y Operation range upper limit float FP Y Measurement range lower limit float FP Y Measurement range upper limit float FP Y not used FP Y Primary channel offset+gain uint FP Y Auxiliary channel offset+gain uint FP Y Calibration coefficients float[17] FP Y Coefficient format uint FP Y not used FP Y 18

21 Service configuration Offset trim float SP Y Span trim float SP Y Measurement time code uchar SP Y not used SP Y 19

22 Holding registers map - continued Section name User configuration Misc Measured variables Datalogger section Register no. Register name Data type Access control Stored in EEPROM Modbus slave address uchar UP Y Group assignment register uchar UP Y Default operation mode uchar UP Y for internal use, do not change UP Y Password ulong N N not used N N Primary chan. direct readout int N N Auxiliary chan. direct readout int N N Conversion coefficients float[4] N N Pressure uint N N Status register uint N N not used N N Delay uint N N Period uint N N Number of samples uint N N Data memory uint[80] N N Memory locations marked in column Stored in EEPROM as Y can be stored into the transmitter s non-volatile EEPROM memory by Write EEPROM function (see paragraph 4.4.3). The stored configuration is recalled after power-up or by Read EEPROM function (see paragraph 4.4.4). Memory locations marked in column Access control as N can be read and written with no restrictions. Memory locations marked as FP (Factory password), SP (Service password) and UP" (User password) can be written only when the proper section is unlocked. The unlocking procedure is described in paragraph Memory locations marked as RO (Read only) cannot be changed Factory configuration section This section contains a basic information about the transmitter and calibration data. The parameters are entered during manufacturing and calibration procedures and cannot be changed by the user. Hardware revision number identifies a version of the transmitter s hardware. Software revision number identifies a version of the transmitter s software. MSB indicates a main revision number, LSB sub-revision number. Serial number identifies each transmitter individually. 20

23 Sensor type. Information about the type of the sensor. Used codes are listed in the following table: Code 01h 02h Sensor type Absolute pressure sensor Relative pressure sensor Units. Information about physical units used for Measurement and Operation range limits representation. Used codes are listed in the following table: Code 02h 03h 04h 05h 07h Units Pa kpa MPa PSI bar Measurement range lower and upper limit specifies pressure values which are measured with the stated accuracy. Operation range lower and upper limit specifies pressure values which are correctly handled by the transmitter s analog-to-digital converter and subsequent numerical calculations. If the pressure value is outside the measurement range but inside the operation range, the measurements are still performed but the accuracy is undefined. Standard values: Transmitter range Measurement range [kpa] Operation range [kpa] (information on label) lower limit upper limit lower limit upper limit kpa abs kpa abs kpa abs kpa abs kpa abs kpa rel kpa rel kpa rel kpa rel kpa rel kpa rel kpa rel kpa rel kpa rel

24 Primary channel offset and gain specifies an offset and gain of the analog-to-digital converter when voltage related to the pressure is measured. The offset is stored in the MSB of the register, the gain in the LSB. Auxiliary channel offset and gain specifies an offset and gain of the analog-to-digital converter when voltage related to the temperature is measured. The offset is stored in the MSB of the register, the gain in the LSB. Calibration coefficients are used to calculate actual pressure using values obtained from the analog-to-digital converter for the primary and auxiliary channel. Coefficient format specifies a layout of the coefficients and algorithm for calculation Service configuration section Parameters in the Service configuration section allows to adjust the offset and span of the transmitter and set the measurement time. The default parameters are entered during calibration procedures and can be changed only by an authorized person using Service password. Offset trim is an additive constant which defines the shift of the transmitter characteristics relative to the factory calibration data. When the transmitter is factory calibrated, the Offset trim is set to During the field calibration a non-zero constant can be written into Offset trim registers to compensate for possible characteristics deviation. Span trim is a multiplicative constant which defines the change of the slope of the transmitter characteristics relative to the factory calibration data. When the transmitter is factory calibrated, the Span trim value is set to During the field calibration a constant can be written into Span trim registers to compensate for possible characteristics deviation. Measurement time code For the firmware version 2.00 and higher the measurement time is set to the fixed value 50 ms and cannot be changed. Any value written to this register has no effect User configuration section User configuration section contains parameters used for Modbus network setup. Parameters are intended to be modified by the user. The section is protected by the User password to prevent accidental change of settings. Modbus slave address contains address to which the transmitter responds. When entering a new address, this is valid immediately after writing to this register. Group assignment register defines to which group(s) the transmitter belongs. Transmitters belonging to the same group can be forced to start measurement simultaneously by a single Start measurement with mask command transmitted as broadcast as described in paragraph Default operation mode specifies whether the transmitter after power-up or reset starts the continuous pressure measurement or not. When changing this register, Write EEPROM command must be issued to store the change in the EEPROM memory. 22

25 Code 00h 01h Default operation mode standby continuous measurement Miscellaneous This section contains registers used for password manipulation. Password. After writing correct value to the password registers, desired section can be unlocked for writing by Unlock section function (see paragraph and 4.4.9) Measured variables In this section, measured and calculated variables are stored. All variables are updated at the end of each single pressure measurement. Primary and auxiliary channel direct readout store values measured directly by the analog-to-digital converter without any further processing. The values are presented just for service purposes and are not intended to be processed by user. Conversion coefficients stores auxiliary coefficients calculated during the measurement. The values are presented just for service purposes and are not intended to be processed by user. Pressure stores actual measured pressure. The value is linearly scaled between Operating range lower limit and Operating range upper limit. Pressure in the physical units can be calculated using formula p = Pressure / * (Operation range upper limit - Operation range lower limit) + + Operation range lower limit where Pressure is the value read form the register 40082, Operation range lower limit is the value read from registers and Operation range upper limit is the value read from registers Status register stores information about transmitter s status. Description of the particular bits is given in the following table: Bit Name Description 15 EEPROM error The bit is set if the internally generated EEPROM checksum does not match the stored value. Possible malfunction of the transmitter may be expected in this case (see sections and 4.4.4) 14 Sensor error The bit is set if sensor or AD converter failure is detected. Pressure readout cannot be considered as reliable in this case. The bit is reset automatically as soon as the correct operation is recovered (see section 4.4.6) 13 Out of range The bit is set if the measured pressure is outside the measurement range. The measurement accuracy is lower compared to the specified. 12 Timing error The bit is set when timing error during datalogging is detected (see section 4.5.5) 23

26 11 Data memory overflow The bit is set when the data memory overflows. This can happen when the datalogging is in progress and master fails to read and erase the stored data quickly enough (see sections and 4.5.6) 4-10 Not used 3 Continuous mode The bit is set when the transmitter is in continuous measurement mode (see section 4.4.7) 2 Start command received The bit is set after receiving the Start measurement command. Master can test this bit to determine whether Start command transmitted as broadcast was accepted by the transmitter. The bit is reset after the first Read multiple registers command (see section 4.4.6) 1 Datalogging in progress The bit is set as long as the datalogging is in progress (see section 4.5.5) 0 Measurement in progress The bit is set as long as the pressure measurement is in progress. The master can poll this bit to determine end of the measurement (see section 4.4.6) Datalogger section Datalogger registers store the values measured during datalogging and a few related parameters. The detailed description of using the transmitter as a datalogger is given in the paragraph Delay stores copy of the Delay parameter passed by the Synchronize Datalogging command. Period stores copy of the Period parameter passed by the Synchronize Datalogging command. Number of samples gives the actual number of samples stored in the Data memory. Data registers store pressure samples measured during datalogging. The registers are being filled starting with register and continuing towards higher register numbers. The oldest sample can be found in the register 40088, the most recent one in the register Most recent sample register no. = Number of samples - 1. Each sample is represented as unsigned integer which can be converted to pressure in physical units using formula given in paragraph

27 4.3.8 Data types A few different data types are used to represent various parameters stored in the transmitter s memory: uchar 8-bit unsigned value. Range form 0 to The 8 bit value is stored in the Least significant byte of the 16 bit register. The most significant byte of the 16 bit register is ignored however it is recommended to write it always as 0x00. int 16-bit signed value in 2 s complement format. Range from to uint 16-bit unsigned value. Range from 0 to ulong 32-bit unsigned value stored in two subsequent 16-bit registers. Higher order bits are stored in register n, lower order bits in register n+1. Range from 0 to float 32-bit single precision floating point value stored in two subsequent 16-bit registers. Register n, [EEEE EEEE SMMM MMMM] exponent (offset 129), sign and mantisa Register n+1, [MMMM MMMM MMMM MMMM] mantisa examples: is coded as 8748h, 8000h is coded as 84C8h, 0000h is coded as 8249h, 0E56h 25

28 4.4 Discrete outputs map Discrete outputs (coils) can by set by the Force single coil (05h) command. Discrete outputs address space is accessible only for writing. Reading is not supported. Physically, the transmitter does not have any discrete outputs. Discrete outputs address space is implemented to allow access to several functions. Forcing a particular discrete output into ON state starts the assigned function (starts a single measurement, for example) Overview of the discrete outputs map Modbus coil numbers shown in the text are in the 0xxxx format which follow the Modicon protocol specification for data items addressing. The actual coil address sent in the Modbus message frame is the coil number shown in the text minus 1. The following table shows the discrete outputs map of the transmitter. Individual functions are described in the subsequent paragraphs. Coil no. Coil / Function name 0001 Reset 0002 Write EEPROM 0003 Read EEPROM 0004 Stop measurement 0005 Start single measurement 0006 Start continuous measurement 0017 Unlock user configuration section 0018 Unlock service configuration section 0025 Change user password 0026 Change service password Master reset Forcing the Master reset coil ON performs a software reset of the transmitter. This is similar to shutting off the power and then reapplying power. The Master reset takes approximately 100 milliseconds to complete. The force master reset coil ON query is not responded Write EEPROM Forcing the Write EEPROM coil ON writes copy of the registers to into EEPROM memory. The registers to hold the transmitter s configuration which is recalled after power-up or by function Read EEPROM. Write cycle takes 220 ms to complete. Any query received during this time is responded with Exception response code 06 Slave device busy Read EEPROM Forcing the Read EEPROM coil ON recalls transmitter s configuration from the EEPROM memory and stores it into registers to Read cycle takes 30 ms to complete. Any query received during this time is responded with Exception response code 06 Slave device busy. 26

29 When the data stored in EEPROM are suspected to be corrupted (internally generated checksum does not match the stored value), bit 15 (EEPROM error) in the Status register is set to indicate possible malfunction of the transmitter Stop measurement. Forcing the Stop measurement coil ON stops the single measurement, continuous measurement or datalogging if this is in progress otherwise the function has no effect Start single measurement. Forcing the Start measurement coil ON starts a single measurement of pressure. The query is responded immediately, but the measurement can take from 30 to 650 ms depending on the requested resolution. During the time when the measurement is in progress, bit 0 (Measurement in progress) in the Status register is set. Polling this bit enables a host to determine the end of the measurement. After the measurement is completed, bit 14 in the Status register is set when a sensor or analog-to-digital converter failure is detected. A typical procedure executed by the master to measure pressure is shown in Figure 8. The master sends a query with the function Start measurement. The transmitter responds and starts the measurement simultaneously. After receiving the response, the master waits until the measurement is finished. The master can either wait for a fixed time which is equal or longer than the measurement time (see paragraph 4.3.3) or it can poll bit 0 (Measurement in progress) of the Status register to determine the end of the measurement (see paragraph 4.3.6). When the measurement is complete, the master reads the value of measured pressure using Read multiple registers command for register Figure 8. Using of Start measurement command Start continuous measurement. Forcing the Start continuous measurement coil ON starts a continuous measurement of pressure. During the continuous measurement mode, the pressure measurements are started and measured variables are updated automatically at the fastest possible rate. The update rate depends on selected resolution as described in the paragraph During the continuous measurement, bit 3 (Continuous mode) in the Status register is set. 27

30 If the continuous measurement mode is required to be entered automatically after power-up or reset, value 0x01 should be written into the Default operation mode register (register no ) and Write EERPOM command must be issued Unlock user configuration section Forcing the Unlock user configuration section coil ON unlocks the user configuration section of registers for write operation. To unlock and write into the User configuration section, the following procedure has to be executed: 1. Write correct password into registers using the Write multiple registers command 2. Force coil 0017 (Unlock user configuration section) ON. If the password is correct, the normal response is returned and the desired section is unlocked. If the password is incorrect, the exception response 03 Illegal data is returned and the section remains locked. 3. Write memory locations in the User configuration section by the Write multiple registers command. The section is then unlocked only for one Write multiple registers command. After the Write command is complete, the section is locked automatically. If another write to the protected section is required, the steps 1 to 3 must be repeated Unlock service configuration section Forcing the Unlock service configuration section coil ON unlocks the service and user configuration sections of registers for write operation. To unlock and write into the User configuration section, the following procedure has to be executed: 1. Write correct password into registers using the Write multiple registers command 2. Force coil 0018 (Unlock service configuration section) ON. If the password is correct, the normal response is returned and the desired section is unlocked. If the password is incorrect, the exception response 03 Illegal data is returned and the section remains locked. 3. Write memory locations in the service and / or user configuration section by the Write multiple registers command. The section is then unlocked only for one Write multiple registers command. After the write command is complete, the section is locked automatically. If another write to the protected section is required, the steps 1 to 3 must be repeated. 28

31 Change password Forcing the Change user password coil or Change service password coil ON changes password for the particular section of registers. The change password procedure is similar for both section passwords, therefore only the Change user password function is described. To change user password, the following procedure has to be executed: 1. Write the old password into registers using the Write multiple registers command. 2. Force coil 0017 (Unlock user configuration section) ON. If the password is correct, the normal response is returned and the change password function is enabled. If the password is incorrect, the exception response 03 Illegal data is returned and change password function is disabled. 4. Write the new password into registers by the Write multiple registers command. 5. Force coil 0025 (Change user password) ON. If the change password function has been enabled in step 2, the password is changed and immediately stored into EEPROM together with a copy of the holding registers If the change password function has been disabled in step 2, the exception response 03 - Illegal data is returned and change password is not performed. The old password remains valid. Setting the user or service password to 0 unlocks the particular section permanently. In this case no unlocking procedure is required before writing into the section. Normal operation is restored as soon as the password is changed to any non-zero value. User and service passwords are both set to 0 when the transmitter is shipped from factory. 29

32 4.5 Modbus function codes Three standard function codes are implemented to access the transmitter s memory and simple functions: Function code (hex) Function 03 Read multiple registers 05 Force single coil 10 Write multiple registers Four non-standard function codes are implemented to allow easy and efficient access to special functions of the transmitter: Function code (hex) Function 45 Start measurement with mask 46 Synchronize datalogging 47 Erase data 48 Set slave address The implemented functions are described in the following paragraphs including example queries and responses. Normal responses are shown. If an error is found during the query processing, an exception response is generated by the transmitter as described in section Read multiple registers (03h) Reads the contents of transmitter s registers. Broadcast is not supported. The query specifies the starting register and quantity of registers to be read. Here is an example of the request to read holding registers from the transmitter with slave address 11h: Byte no. Field name Example (hex) 1 Slave address 11 2 Function code 03 3 Starting address (Hi) 00 4 Starting address (Lo) 30 5 Number of registers (Hi) 00 6 Number of registers (Lo) 03 7 CRC (Lo) xx 8 CRC (Hi) xx 30

33 The response contains data read from the specified registers. The register data in the response message are packed as two bytes per register. For each register, the first byte contains the most significant byte and the second contains the least significant byte. An example of the response to the query: Byte no. Field name Example (hex) 1 Slave Address 11 2 Function Code 03 3 Number of Data Bytes 06 4 Contents of register 30h MSB 00 5 Contents of register 30h LSB 01 6 Contents of register 31h MSB C8 7 Contents of register 31h LSB 00 8 Contents of register 32h MSB F3 9 Contents of register 32h LSB CRC (Lo) xx 11 CRC (Hi) xx Force single coil (05h) Forces a single coil to either ON or OFF state. Forcing the particular coil ON initiates assigned function as described in paragraph 4.4. When broadcast, the function is performed in all attached slaves. The query specifies the coil address (function). The requested ON / OFF state is specified by a constant in the query data field. A value FF00h requests to perform function. A value 0000h means no action. Here is an example of the request to initiate the Write EEPROM function (coil no. 0002) for the transmitter with slave address 11h: Byte no. Field name Example (hex) 1 Slave address 11 2 Function code 05 3 Coil address (Hi) 00 4 Coil address (Lo) 01 5 Force data (Hi) FF 6 Force data (Lo) 00 7 CRC (Lo) xx 8 CRC (Hi) xx 31

34 The normal response is an echo of the query. Here is an example of the response to the query shown above: Byte no. Field name Example (hex) 1 Slave address 11 2 Function code 05 3 Coil address (Hi) 00 4 Coil address (Lo) 01 5 Force data (Hi) FF 6 Force data (Lo) 00 7 CRC (Lo) xx 8 CRC (Hi) xx Write multiple registers (10h) Writes data into a sequence of specified registers. When broadcast, the function writes the same registers in all attached slaves. If an attempt is made to write at least some of the data into password-protected sections, no data are written and exception response Illegal address is generated (see paragraph 0). The query specifies the registers to be written. The requested data values are specified in the query data field. Here is an example of the request to write data in registers of the transmitter with slave address 11h: Byte no. Field name Example (hex) 1 Slave address 11 2 Function code 10 3 Starting address (Hi) 00 4 Starting address (Lo) 42 5 Number of registers (Hi) 00 6 Number of registers (Lo) 02 7 Number of data bytes 04 8 Data to register 42h - MSB 4A 9 Data to register 42h - LSB 0C 10 Data to register 43h - MSB Data to register 43h - LSB C8 12 CRC (Lo) xx 13 CRC (Hi) xx 32

35 The normal response returns the slave address, function code, starting address, and number of registers written. Here is an example of the response to the query shown above: Byte no. Field name Example (hex) 1 Slave address 11 2 Function code 10 3 Starting register (Hi) 00 4 Starting register (Lo) 42 5 Number of registers (Hi) 00 6 Number of registers (Lo) 02 7 CRC (Lo) xx 8 CRC (Hi) xx Start measurement with mask (45h) Starts single measurement of pressure for selected transmitters. For multidrop configuration, the following algorithm was implemented to allow multiple transmitters to be started by a single Start measurement with mask command transmitted as broadcast. Transmitters on the bus can be individually assigned to one or multiple groups by setting corresponding bit in the Group assignment register Up to 7 different groups can be created. Beside this, all transmitters belong to group 0 by default (bit 0 in the Group Assignment Byte is always considered to be set regardless its real state). Transmitters assigned to the same group can be started simultaneously by a Start measurement with mask command transmitted as broadcast. The group mask byte transmitted in this query specifies which group(s) of transmitters will start a single measurement. Every transmitter makes logical AND between Group mask byte in the received query and Group assignment register. If the result is non-zero, the transmitter starts single measurement. The query is responded immediately, but the measurement can take from 30 to 650 ms depending on the requested resolution. During the time when the measurement is in progress, bit 0 (Measurement in progress) in the Status register is set. Polling this bit enables the host to determine the end of the measurement. After the measurement is completed, bit 14 (Sensor error) in the Status register is set when sensor or analog-to-digital converter failure is detected. Here is an example of the request to start single measurement for all transmitters assigned to groups 2 and 7. No response is generated for the broadcast frame. Byte no. Field name Example (hex) 1 Slave address 00 2 Function code 45 3 Group mask 84 4 CRC (Lo) xx 5 CRC (Hi) xx 33

36 4.5.5 Synchronize datalogging (46h) The transmitter is able to automatically measure pressure in preset time intervals and store the values into the registers (datalogging). Synchronize Datalogging command can be used to start or re-synchronize the datalogging. The query specifies Period parameter which describe measurement timing. If no datalogging is in progress, the Synchronize Datalogging command starts it. The first pressure measurement is initiated immediately after receiving the query. The next measurements are then initiated in regular intervals defined by the Period value. If datalogging is already in progress, the Synchronize Datalogging command re-synchronize the internal time base. The oncoming measurement is expedited in order to start immediately after receiving the query. The next measurements are again initiated in regular intervals defined by Period value. Figure 9 illustrates using of the Synchronize Datalogging command. Synchronize datalogging Synchronize datalogging Communication Query Response Query Response Measurement Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Period Period Period Figure 9. Using of Synchronize datalogging command. Bit 1 (Datalogging in progress) in the Status register is set during datalogging. When the data memory is full, datalogging is stopped automatically, bit 11 (Data memory overflow) in the Status register is set and bit 1 (Datalogging in progress) is reset. If the Period parameter is set too short with respect to the time of measurement, the measurements are initiated as fast as possible and bit 12 (Timing error) in the Status register is set to indicate error. Value of the Period parameters can be calculated using formula: Period = 128.t-1, where t is time of the period in seconds. Generally speaking, the period value can be also set anywhere from 1/128 s to 512 s (0000h to FFFFh) with resolution of 1/128 s, but the minimum reasonable period for datalogging is determined by the time of single measurement which is set to 50 ms. Datalogging can be stopped at any moment by Stop measurement function, see chapter Time 34