CALIBRATION PROCEDURE FP-RTD-122 Version 2.0 Introduction This document contains step-by-step instructions for calibrating the National Instruments FP-RTD-122 module. The procedure contains the following five sections: Introduction This section explains what calibration is, why you should calibrate your devices, and how often you should calibrate. Equipment and Other Test Requirements This section contains information on test equipment, documentation, software, and test conditions required for calibration. Calibration Procedures This section contains step-by-step instructions for verifying and adjusting the FP-RTD-122 module. This section also includes the C/C++ functions you use to verify and adjust the FP-RTD-122 module, and instructions on how to use them. Additional Module Information: FP-RTD-122 This section contains flowcharts that outline the verification and adjustment procedures, and information on additional utility functions for the FP-RTD-122 module. Calibration-Specific Errors in FieldPoint This section contains a list of common calibration error codes for the FP-RTD-122 modules. You should use this calibration procedure in conjunction with the calibration software library that is included with the documentation. The software library contains specific functions required for calibrating the module. FieldPoint, National Instruments,NI, and ni.com are trademarks of National Instruments Corporation. Product and company names mentioned herein are trademarks or trade names of their respective companies. 370352A-01 Copyright 2001 National Instruments Corp. All rights reserved. July 2001
What Is Calibration? Why Should You Calibrate? How Often Should You Calibrate? Calibration consists of verifying the measurement accuracy of a device and adjusting for any measurement error. Verification is measuring the performance of the device comparing these measurements to the factory specifications. During calibration, you supply and read voltage levels using external standards, then you adjust the module calibration constants. The new calibration constants are stored in the EEPROM. These calibration constants are loaded from memory as needed to adjust for the error in the measurements taken by the device. The accuracy of electronic components drifts with time and temperature, which can affect measurement accuracy as the device ages. Calibration restores these components to their specified accuracy and ensures that the device still meets National Instruments (NI) standards. The measurement requirements of your application determine how often the FP-RTD-122 module needs to be calibrated to maintain accuracy. NI recommends that you perform a complete calibration at least once every year. You can shorten this interval to 90 days or six months based on the demands of your application. Equipment and Other Test Requirements This section describes the equipment, test conditions, documentation, and software you need to calibrate the FP-RTD-122 module. Test Equipment Calibrating an FP-RTD-122 module requires using a high-precision voltage source that is accurate to at least 20 ppm (0.002%). NI recommends that you use the following instruments for calibration: Calibrator Fluke 5700A DMM Hewlett Packard 3458A FieldPoint FP-1000 network module FieldPoint calibration base model FP-TB-CAL, part number 777519-90, that allows you to write new calibration constants to the module EEPROM 11-24 V power supply NI PS-2 power supply RS-232 serial cable FP-RTD-122 Calibration Procedure 2 ni.com
If a Fluke 5700A is not available, use the 100 ppm accuracy specification to choose a substitute calibration standard. Test Conditions Documentation Follow these guidelines to optimize connections and test conditions during calibration: Keep connections to the module short. Long cables and wires act as antennae, picking up extra noise that can affect measurements. Use shielded copper wire for all cable connections to the device. Use twisted-pair wire to eliminate noise and thermal offsets. Maintain a temperature between 18 and 28 C. To operate the module at a specific temperature outside this range, calibrate the module at that temperature. Keep relative humidity below 80%. Allow a warm-up time of at least 15 minutes to ensure that the measurement circuitry is at a stable operating temperature. This section describes the documentation you need to calibrate the FP-RTD-122 module. In addition to this calibration procedure, you may need to refer to the following documentation: FP-1000/1001 Programmer Reference Manual FP-RTD-122 Operating Instructions FP-1000/1001 User Manual FP-1000/1001 Quick Start Guide You can download these documents from ni.com/manuals. Software Calibrating the FP-RTD-122 module requires using the calibration software library, which you downloaded or received with this documentation. The library contains function calls that perform specific tasks during the calibration procedure. If you do not have the software library files, you can download them from ni.com/calibration. National Instruments Corporation 3 FP-RTD-122 Calibration Procedure
Writing Your Calibration Procedure The Calibration Procedures section later in this document provides step-by-step instructions for calling the appropriate calibration functions. The calibration software library consists of the following files: fpcalibration.dll fpcalibration.h Refer to the Flowcharts for Creating Verification and Adjustment Code section for illustrations of the code used at each step of the calibration procedure. Throughout this procedure, you send commands to the FieldPoint bank. These commands consist of strings of ASCII characters that cause the module to perform various functions during verification and adjustment. The FP-1000/1001 Programmer Reference Manual contains details on the format of these commands. You construct and send commands that set the attributes of the module, read 12-bit data (input modules), and write 16-bit data (output modules). To communicate with the module, you need to configure the module address and baud rate using the switches on the interface module. Understanding the Calibration Functions The file fpcalibration.dll contains four main functions that the user program calls to start a calibration session, perform verification, make adjustments, and end the calibration session. The following paragraphs describe each of the calibration functions and explain how they are used. int fp_calstart int fp_calstart(int portnum, int device, unsigned long baudrate, char* password, int passwordsize, char reserved, sessionhandle* m_session); This function starts the calibration session. Use this function every time you need to either verify or adjust a module. The parameters for this function are described in detail in detail in the Calibration Procedures section later in this document. int fp_calverify int fp_calverify(sessionhandle m_session, int measurementmode, int range, int channel, double* data, int datasize); This function takes data for one channel and verifies that it is within the acceptable operating ranges. The function returns a 0 if the data is within specifications. The data parameter is a pointer to an array of data in the FP-RTD-122 Calibration Procedure 4 ni.com
format shown in Figure 1. The other parameters for this function are described in detail in the Calibration Procedures section of this document. Low-Resistance Reading from FP-RTD-122 Mid-Resistance Reading from FP-RTD-122 High-Resistance Reading from FP-RTD-122 int fp_caladjust Figure 1. ArrayofDataUsedbyfp_CalVerify int fp_caladjust(sessionhandle m_session, int measurementmode, int range, int channel, double* data, int datasize); This function uses the data for one channel to calculate new calibration constants. The function returns a 0 if the new constants for the channel you are calibrating were calculated successfully. The data parameter is a pointer to an array of data in the format shown in Figure 2. The other parameters for this function are described in detail in the Calibration Procedures section of this document. Low-Resistance Actual Value from Calibrator Low-Resistance Reading from FP-RTD-122 High-Resistance Actual Value from Calibrator High-Resistance Reading from FP-RTD-122 Figure 2. ArrayofDataUsedbyfp_CalAdjust National Instruments Corporation 5 FP-RTD-122 Calibration Procedure
int fp_calend int fp_calend(sessionhandle m_session, int action); This function terminates the calibration or verification session. A 0 is returned if the function is used to terminate a session and write new constants to the EEPROM. The parameters for this function are described in detail in the Calibration Procedures section of this document. Understanding FieldPoint Commands In addition to the four calibration functions, you also use three FieldPoint commands to calibrate the FP-RTD-122 module. Power Up Clear, Set Attributes, and Read 16-bit Data are explained in the next three sections. Note Read the FieldPoint Commands Overview section of the FP-1000/1001 Programmer Reference Manual before you write the commands to make sure you understand the syntax for each command. Power Up Clear Command Syntax A Example >01A??[cr] All FieldPoint commands have similar syntax and contain the following five fields: [start][address][command][checksum][end] The Power Up Clear command is the first command you send after applying power to the module. This command prevents the FP-RTD-122 module from returning a power-up clear expected error message (E_PONCLR_EXP). This command functions only if it is the first command you send after power-up. where > = the [start] character of any FieldPoint command 01 = the module address A = the actual command?? = the checksum [cr] = carriage return FP-RTD-122 Calibration Procedure 6 ni.com
Note Sending?? instead of the actual checksum is valid, but FieldPoint will not do error checking. Refer to Chapter 1, FieldPoint Commands Overview, ofthefp-1000/1001 Programmer Reference Manual for more detailed information on the command fields. Set Attributes Command The Set Attributes command sets the specified attributes and range for each specified channel of the module you are addressing. Syntax!D[positions]{[attrMask][rangeMask][settings]}[cr] Example Assume you are changing the range of channel 3 to ±50 mv. The command would be: >01!D0008000010A??[cr] where > = the [start] character of any FieldPoint command 01 = the module address!d = the actual command 0008 = four ASCII-hex characters representing [positions], or the channel you are targeting with this command (channel 3 in this example) 0000 = four ASCII-hex characters representing [attrmask] for channel 0 1 = one ASCII-hex character representing [rangemask]; a zero in this field indicates that the range is not affected 0A = two ASCII-hex characters representing the [settings] entry; 0A corresponds with the ±50 mv range?? = the checksum [cr] = carriage return If you need more information on the parameter values to use in the Set Attributes command, refer to the tables in Chapter 5, Extended FieldPoint Command Descriptions, inthefp-1000/1001 Programmer Reference Manual. Table 1 lists the ASCII-hex conversions to use in the positions parameter. National Instruments Corporation 7 FP-RTD-122 Calibration Procedure
Table 1. Values for the positions Parameter for FP-RTD-122 Channel ASCII Characters 0 0001 1 0002 2 0004 3 0008 4 0010 5 0020 6 0040 7 0080 Read 16-Bit Data Command The Read 16-bit Data command reads data from targeted input and output channels of the module you are addressing. Each data value is a 16-bit value. Syntax!F[positions] Example Assume you are reading from channel 3. The command would be: >01!F0008??[cr] where > = the [start] character of any FieldPoint command 01 = the module address!f = the actual command 0008 = four ASCII-hex characters representing [positions], or the channel you are targeting with this command (channel 3 in this example)?? = the checksum [cr] = carriage return The ASCII-hex values to use in the [positions] parameterareshownintable1. FP-RTD-122 Calibration Procedure 8 ni.com
Calibration Procedures Configuring the FP-RTD-122 Module Calibration consists of four main steps: 1. Configuring the module for calibration. This step is described in the Configuring the FP-RTD-122 Module section. 2. Verifying the existing performance of the module. This step, which is described in the Verifying the Performance of the FP-RTD-122 Module section, determines whether the module is operating within its specified range prior to making adjustments. 3. Adjusting the calibration constants of the module using a high-precision voltage source. This step is described in the Adjusting the FP-RTD-122 Module section. 4. Verifying again to ensure that the module is operating within its specifications after adjusting. These steps are described in detail in the following sections. To verify the operation of the test fixture, build a FieldPoint bank with a network module, calibration terminal base, power supply, and the module you are calibrating. Then, complete the following steps: 1. Place the FP-RTD-122 module in the calibration terminal base. 2. Connect the bank to the host computer using an RS-232 serial cable. 3. Launch FieldPoint Explorer and add a communication resource to the server by right-clicking FieldPoint and selecting Add a Comm Resource to this Server. 4. Make sure the correct communication port and baud rate appear in the dialog box, then click Find Devices. 5. Expand the view to show the devices found. You should see the module you want to calibrate. If you do not, the network module is not communicating correctly with either the host or the FP-RTD-122 module. 6. Close FieldPoint Explorer before you go on to the next section. Caution You must close FieldPoint Explorer after configuring the FP-RTD-122 module. FieldPoint Explorer must remain closed when you call calibration functions to prevent a system crash. You have finished configuring the FP-RTD-122 module and verifying communication between the module and the calibration system. If you need additional information on configuring the FP-RTD-122 module, refer to the module operating instructions or the FP-1000/1001 Quick Start Guide. National Instruments Corporation 9 FP-RTD-122 Calibration Procedure
Verifying the Performance of the FP-RTD-122 Module This procedure determines how well the FP-RTD-122 module is meeting its specifications. To complete this procedure, you need a calibrator to verify values and the FP-1000/1001 Programmer Reference Manual. Make sure that you have read the Equipment and Other Test Requirements section earlier in this document before beginning this procedure. Complete the following steps to verify the performance of the FP-RTD-122 module: 1. Configure and open a connection to the interface module through your program. Opening a connection allows you to send FieldPoint commands to the module you want to calibrate. For detailed information on using FieldPoint software, refer to Chapter 4, Installing and Using FieldPoint Software in the FP-1000/1001 User Manual. 2. Connect one wire from one pair of the calibrator output to the EXCITE terminal for channel 0. Refer to Table 2 to determine the correct terminal number. Channel Table 2. FP-RTD-122 Terminal Assignments Terminal Numbers EXCITE SENSE COM 0 1 2 18 1 3 4 20 2 5 6 22 3 7 8 24 4 9 10 26 5 11 12 28 6 13 14 30 7 15 16 32 3. Connect one wire of the second pair of the calibrator output to the SENSE terminal for channel 0. 4. Connect the other wire of the second pair of the calibrator output to the COM terminal for channel 0. 5. Ensure that all other terminals on the calibration base are open. 6. Set the calibrator to apply the first value listed in the Test Point column in Table 3. Note Use the first value in the Test Point column for the first test. When you repeat this step for other values, use the successive values listed in the Test Point column. FP-RTD-122 Calibration Procedure 10 ni.com
Range Range ID Table 3. FP-RTD-122 Module Specifications Location Test Point Value (ohms) Lower Limit (ohms) Upper Limit (ohms) 0 400 Ω 30 +FS 190 189.856 190.144 ZS 100 99.874 100.126 FS 10 9.892 10.108 0 4000 Ω 31 +FS 1900 1898.56 1901.44 ZS 1000 998.74 1001.26 FS 100 98.92 101.81 The next two steps use the FieldPoint commands Set Attributes and Read Analog Inputs. Refer to the section Understanding FieldPoint Commands for the description and syntax of each command. 7. Use the Set Attributes command to configure the channels for the appropriate range using the Range ID (settings) in Table 3 from the same row you used in step 6. Set the following parameters: positions 0001 attrmask 0000 rangemask 1 settings The Range ID value from Table 3 8. Use the Read 16-bit Data command to acquire one point of binary data and store the result. Set positions to 0001. 9. Record the reading from step 8 in a variable. 10. Repeat steps six through nine to obtain data for each Test Point value listed in Table 3, including both 400 Ω and 4000 Ω ranges. Note You only need to verify the readings for each range on one channel. 11. Start a calibration session by calling fp_calstart with the following parameters: port The serial port used to connect to the FP-1000 network module: 1 for COM1, 2 for COM2, and so on device The address of the I/O module to verify or calibrate. If the module is the first module to the right of a network module with a base address of 0, its address is 1 baudrate The baud rate used to communicate with the network module National Instruments Corporation 11 FP-RTD-122 Calibration Procedure
password A four-character string containing the module password; the default password is NATI caller 0 m_session A pointer that is returned when you call this function, contains the handle to reference to the current communications session; use this handle with the rest of the calibration functions to reference the same calibration session 12. Call fp_calverify two times, once for each range. Use the data from channel 0 to verify that the FP-RTD-122 module readings for both ranges are within specifications. The parameters for fp_calverify are as follows: m_session The session handle you obtained with the fp_calstart function measurementmode 1 range The Range ID value from Table 3, depending on the range you are verifying channel 0 datasize 3 data A pointer to the array of data in the format shown in Figure 1 If the fp_calverify function returns a 0, the module is within specification. If the function returns a 1, the module is out of specification and requires adjustment. 13. Call fp_calend to end the calibration session. Set the action parameter to 1 so the values are not written to the EEPROM. 14. Disconnect the calibrator from the module. You have finished verifying the performance of the FP-RTD-122 module. If all ranges are within the module specifications, you are finished calibrating the FP-RTD-122 module. If any ranges are outside the module specifications, you must adjust the calibration constants as described in the Adjusting the FP-RTD-122 Module section of this document. FP-RTD-122 Calibration Procedure 12 ni.com
Adjusting the FP-RTD-122 Module The procedure for adjusting the calibration constants in the FP-RTD-122 is divided into three main sections: Measuring 400 Ohm Range Values This section describes how to measure values for the 400 Ω range of the FP-RTD-122 module. Measuring 4000 Ohm Values This section describes how to measure values for the 4000 Ω range of the FP-RTD-122 module. Writing New Calibration Constants to the EEPROM This section describes how to use measurements from the two previous sections to write new calibration constants to the EEPROM of the FP-RTD-122 module. Measuring 400 Ohm Range Values To measure values for the 400 Ω range of the FP-RTD-122 module, complete the following steps: 1. Connect one wire from one pair of the calibrator output to the EXCITE terminal for channel 0 (terminal 1). 2. Connect one wire of the second pair of the calibrator output to the SENSE terminal for channel 0 (terminal 2). 3. Connect the other wire of the second pair of the calibrator output to the COM terminal for channel 0 (terminal 18). 4. Use the Set Attributes command to configure the FP-RTD-122 module for the 400 Ω range using the corresponding Range ID (settings) from Table 3. Set the following parameters: positions 0001 attrmask 0000 rangemask 1 settings 30 5. Set the calibrator to apply 100 Ω to the module input. Store this value as low_ohm_actual for the 400 Ω range. 6. Use the Read 16-bit Data command to acquire and average 16 binary data points. Store this value as low_ohm_value for the 400 Ω range. 7. Set the calibrator to apply 190 Ω to the module input. Store this value as hi_ohm_actual for the 400 Ω range. 8. Use the Read 16-bit Data command to acquire and average 16 binary data points. Store this value as hi_ohm_value for the 400 Ω range. 9. Leave all wires connected and continue to the Measuring 4000 Ohm Values section. National Instruments Corporation 13 FP-RTD-122 Calibration Procedure
Measuring 4000 Ohm Values To measure values for the 4000 Ω range of the FP-RTD-122 module, complete the following steps: 1. Use the Set Attributes command to configure the FP-RTD-122 module for the 4000 Ω range using the corresponding Range ID (settings) from Table 3. Set the following parameters: positions 0001 attrmask 0000 rangemask 1 settings 31 2. Set the calibrator to apply 1000 Ω to the module input. Store this value as low_ohm_actual for the 4000 Ω range. 3. Use the Read 16-bit Data command to acquire and average 16 binary data points. Store this value as low_ohm_value for the 4000 Ω range. 4. Set the calibrator to apply 1900 Ω to the module input. Store this value as hi_ohm_actual. 5. Use the Read 16-bit Data command to acquire and average 16 binary data points. Store this value as hi_ohm_value for the 4000 Ω range. You now have the measurements you need for calculating the new calibration constants. Use these measurements to write the calibration constants to the EEPROM of the module. Writing New Calibration Constants to the EEPROM To write the new calibration constants to the EEPROM, you need to call the calibration functions from the calibration DLL. Complete the following steps: 1. Close any open connections to the FP-RTD-122 module. 2. Call fp_calstart to open a connection to the module and to obtain a session handle. 3. In a loop, call fp_caladjust two times, once for each range. Use the data you collected in the sections Measuring 400 Ohm Range Values and Measuring 4000 Ohm Values. Set the following parameters: m_session The session handle you obtained from fp_calstart measurementmode 4 rangeid 400 or 4000, depending on the range channel The channel you are adjusting, in this case 0 FP-RTD-122 Calibration Procedure 14 ni.com
Verifying After Adjustments datasize 6 data A pointer to an array with the format shown in Figure 1 If the adjustment is successful, the function returns a 0. 4. Call fp_calend with the action parameter set to 0 to write the new value to the EEPROM. If you want to end the session without saving the new calibration constants, set the action parameter to 1. You have completed adjusting the calibration constants for the FP-RTD-122 module. After you have completed adjusting the calibration constants, verify the performance of the FP-RTD-122 module again to ensure that you are using the new calibration constants. 1. Remove the FP-RTD-122 module from the base and reinsert it. You do not need to disconnect the power before removing the module. 2. Repeat the procedure described in the Verifying the Performance of the FP-RTD-122 Module section of this document. You have completed the calibration procedure for the FP-RTD-122 module. Additional Module Information: FP-RTD-122 This section includes flowcharts of the verification and adjustment processes, and detailed information on other supported functions that are part of the calibration software. Flowcharts for Creating Verification and Adjustment Code The following flowcharts show the appropriate commands for verifying and calibrating the FP-RTD-122 module. Refer to the Calibration Procedures section of this document for additional information on the software structure and for function explanations. National Instruments Corporation 15 FP-RTD-122 Calibration Procedure
FP-RTD-122 Analog Input Verification Flowchart Figure 3 shows the flowchart of the process for analog input verification of the FP-RTD-122 module. Use this flowchart to design and write your verification program. From your application, determine the input range to verify. Configure the FP-RTD-122 module using the Set Attributes command. Read the required data using the Read 16-bit Data command. Store data in a variable. All ranges done? No Go to next range. Yes Call fp_calstart. Call fp_calverify. Call fp_calend with the action parameter set to 1. Figure 3. FP-RTD-122 Analog Input Verification Flowchart FP-RTD-122 Calibration Procedure 16 ni.com
FP-RTD-122 Adjustment Flowchart Figure 4 shows the flowchart of the process for adjusting the FP-RTD-122 module. Use this flowchart to design and write your adjustment program. From your application, determine the input range to adjust. Configure the FP-RTD-122 module using the Set Attributes command. Read the required data using the Read 16-bit Data command. Store data in a variable. All ranges done? No Go to next range. Yes Call fp_calstart. Call fp_caladjust. Call fp_calend with the action parameter set to 0. Figure 4. FP-RTD-122 Adjustment Flowchart National Instruments Corporation 17 FP-RTD-122 Calibration Procedure
Additional FP-RTD-122 Module Functions fp_calchangepassword In addition to the functions listed previously, several other utility functions exist within the supplied DLL that you can call for more detailed information. These functions are explained in the following paragraphs: fp_calchangepassword(sessionhandle m_session, char* oldpass, char* newpass) fp_calfetchcount This function changes the current password on the module. The parameters are as follows: m_session The session handle obtained with the fp_calstart function oldpass A pointer to the four-character old password newpass The new four-character password that you program into the module fp_calfetchcount(sessionhandle m_session, int* count) fp_calfetchdate This function returns the number of times the module has been calibrated in the count variable. The parameters are as follows: m_session The session handle obtained with the fp_calstart function count An 8-bit variable that rolls over to 0 after the module has been calibrated 255 times fp_calfetchdate(sessionhandle m_session, int* year, int* month, int* day) This function returns the year, month, and day the unit was last calibrated. The parameters are as follows: m_session The session handle obtained with the fp_calstart function year A pointer to a variable that contains the year the module was last calibrated month A pointer to a variable that contains the month the module was last calibrated day A pointer to a variable that contains the day the module was last calibrated FP-RTD-122 Calibration Procedure 18 ni.com
fp_calfetchmiscinfo fp_calfetchmiscinfo(sessionhandle m_session, char* miscinfo, int buffersize) fp_calreset This function returns the data stored in the miscellaneous information area of EEPROM within the module. The parameters are as follows: m_session The session handle obtained with the fp_calstart function miscinfo The pointer to the data stored in the miscellaneous area of the EEPROM buffersize The size of the miscinfo data, which is 12 bytes for the FP-RTD-122 fp_calreset (sessionhandle m_session) This function resets the calibration constants to their default values and writes them to the EEPROM. This function has only one parameter: m_session The session handle obtained with the fp_calstart function Note Because fp_calreset resets the calibration constants, you must collect new data after calling the function for calibration to be valid. fp_calstoremiscinfo fp_calstoremiscinfo(sessionhandle m_session, char* miscinfo int miscbufsize) This function takes the data in the miscinfo array and stores it to the miscellaneous info area of the EEPROM. The parameters are as follows: m_session The session handle obtained with the fp_calstart function miscinfo A pointer to the data that is stored in the miscellaneous information area of the EEPROM miscbufsize ThesizeofthemiscInfo array,whichisequaltoor less than 12 bytes National Instruments Corporation 19 FP-RTD-122 Calibration Procedure
Calibration-Specific Errors in FieldPoint Table 4 contains a list of common calibration errors for FieldPoint. If a function returns an error that is not listed in Table 4, it is either an optomux error or a FieldPoint error. If you need more information on these errors, refer to the FP-1000/1001 Programmer Reference Manual. Error Table 4. Calibration-Specific Errors in FieldPoint Description 0 Success module calibrated without problems 1 Invalid handle 2 Invalid session handle 3 Communications error 4 Null buffer parameter 5 Improper module 6 Unexpected internal error 7 Handle is already in use 8 Calibration Incomplete 9 Calibration data is corrupted 10 Buffer parameter is too long 11 Invalid channel 12 Invalid range 13 Invalid mode 14 Invalid baudrate 15 Data size error 16 Memory allocation failure 17 Data not initialized 18 Password mismatch 19 Old calibration constants are out of range; you must reset to nominal values using fp_calreset FP-RTD-122 Calibration Procedure 20 ni.com