1-Wire Current Loop Interface. User Manual

Transcription

1 User Manual February 2015

2 Table of Contents 1 Features 3 2 Technical Specifications Board Overview 4 1-Wire Terminal Block Connector (K2) 4 1-Wire RJ45 Connectors (K3, K4) 5 Current Loop Connector (K1) 5 Optional RC Filter Circuit 5 Power Supply 6 1-Wire Connectivity 6 Communications Protocol 6 4 Software Support 7 1-Wire Automation Server 7 ows 7 owfs 8 5 Legal Information 9 Disclaimer 9 Trademarks 9 6 Contact Information 9 Revision History Date Authors Description Peter S'heeren Initial release Peter S'heeren Added section about 1-Wire Automation Server software support. Second release. 2 User Manual

3 1 Features Enables the connection of various industrial sensors (temperature, pressure, load cells,...) to a 1-Wire network. Converts standard industrial current loop signals (4-20 ma) to 1-Wire. Opto-isolated current loop input with overcurrent protection. Power supply 5 V DC 10 ma max. via 1- Wire interface (all other necessary voltages are generated internally by the circuit). Based on DS Wire slave chip. Built with 0.1 % precision resistors (Panasonic ERA series). DS Wire slave chip is powered from a precision 5 V supply for maximum accuracy. 2 Technical Specifications Weight 29 g Dimensions 90 mm x 50 mm x 15 mm (W x D x H) User Manual 3

4 3 Board Overview Mark Label Description 1 K2 1-Wire bus terminal block connector 2 K4 1-Wire bus RJ45 connector 3 K3 1-Wire bus RJ45 connector 4 K1 Current loop connector 5 RX, CX, SJ1 Optional RC filter circuit for signal averaging/smoothing 1-Wire Terminal Block Connector (K2) Mark Description 5V 1W GND 5V 5 V supply 1W 1-Wire DQ line (data) GND Ground 4 User Manual

5 1-Wire RJ45 Connectors (K3, K4) Mark Description 1 Unassigned 2 +5 V power 3 Unassigned 4 1-Wire DQ (data) 5 1-Wire ground 6 Unassigned 7 Unassigned 8 Unassigned Plug top view Receptacle front view All eight pins are routed between the two connectors. The doesn't use the unassigned lines. Current Loop Connector (K1) Mark Description I+ Current loop positive I- Current loop negative I+ I- Connect the current loop to this connector. The current loop is galvanically isolated from the 1-Wire interface. A polyfuse of 160 ma protects the current loop against an overcurrent condition. Nevertheless you should avoid a situation with more than 20 ma on the current loop. The voltage drop over I+ and I- is 6 V maximum with a current of 20 ma. Optional RC Filter Circuit Mark RX CX SJ1 Description Resistor Capacitor Solder jumper If you need to apply signal averaging/smoothing to the conversion results from the current loop interface, you can add an RC filter circuit. Open the solder jumper if you add an RC circuit. Keep the solder jumper closed otherwise. User Manual 5

6 Power Supply The must be externally powered over one of the 1-Wire connectors (K1, K2, or K3). It's important you provide a stable 5 V power supply. You may have to use a power injector if you're using very long 1-Wire cables or if you're using a 1-Wire adapter that doesn't provide enough power on the 5 V line. If you connect multiple 1-Wire Current Loop Interfaces to the same 1-Wire bus, you should use a 1-Wire power injector in order to provide enough power to all devices. 1-Wire Connectivity The provides three connection points for 1- Wire cabling and wiring. The terminal block connector is typically used for wiring the 1-Wire Current Loop Interface to an AbioWire or another 1-Wire adapter. K2 5V 1W GND Terminal block connector The RJ45 receptacles provide a means to set up a 1-Wire bus in daisy chain using UTP cables. K3 RJ45 receptacle K4 RJ45 receptacle Communications Protocol The 1-Wire slave function on the current loop interface is a Maxim DS2438 chip. See the Maxim DS2438 datasheet for more information about the 1-Wire slave chip. The family code of the DS2438 is 26h. Since the family code alone doesn't uniquely identify a, the host system must associate the full 8-byte ROM code with the device. The host system is expected to use Standard speed when communicating with the current loop interface over the 1-Wire bus. The current loop interface converts a current of 4 to 20 ma on K1 to a linear range of 1.9 to 9.5 V. This voltage is presented to the VAD pin of the DS2438 chip. To achieve optimal accuracy, you're advised to convert 4 ma and 20 ma as reference currents and use the resulting voltages for your measurements. If the current is less than 4 ma, the device will still present a voltage on the VAD pin but the result is not guaranteed to be accurate. If there's no current flowing through the current loop, the converted voltage will be zero or very close to zero (typically 0.00 V or 0.01 V). The DS2438 chip incorporates a temperature sensor that software can read out. 6 User Manual

7 4 Software Support 1-Wire Automation Server Use client command Device Sense to read the temperature and voltage levels: dev "26-141BFCE" sense force dev " BFCE" sensed ds2438 " :35: C V 01F V FFF9-0007" You can change the temperature scale by issuing client command Attribute. Example: attr tscale=fahrenheit This command sets the temperature scale to Fahrenheit. The 1-Wire Automation Server GUI program offers a comfortable way to work with the 1- Wire Current Loop Interface in a graphical desktop environment: In the above picture, you can see the temperature and voltage levels of the 1-Wire Current Loop Interface. You can change to another temperature scale immediately by clicking on the radio buttons above the cancel button. ows Software package ows v1.2.0 and later includes program owsrds. This program enables you to read the sensed values from the. Example invocations of the program: #./owsrds -lu -tf -network BFCE This command reads the temperature in Fahrenheit and the VAD voltage level. The returned voltage level represents the value sensed on the current loop interface. User Manual 7

8 owfs It's assumed you're using the filesystem client of the owfs package. In the examples it's supposed you've specified /mnt/onewire/ as the mount directory for the 1-Wire file system. # cat /mnt/onewire/26.cebf /vad This command reads the VAD voltage level. The returned voltage level represents the value sensed on the current loop interface. # cat /mnt/onewire/26.cebf /temperature This command reads the temperature. 8 User Manual

9 5 Legal Information Disclaimer Axiris products are not designed, authorized or warranted to be suitable for use in space, nautical, space, military, medical, life-critical or safety-critical devices or equipment. Axiris products are not designed, authorized or warranted to be suitable for use in applications where failure or malfunction of an Axiris product can result in personal injury, death, property damage or environmental damage. Axiris accepts no liability for inclusion or use of Axiris products in such applications and such inclusion or use is at the customer's own risk. Should the customer use Axiris products for such application, the customer shall indemnify and hold Axiris harmless against all claims and damages. Trademarks All product names, brands, and trademarks mentioned in this document are the property of their respective owners. 6 Contact Information Official website: User Manual 9