ROC364 Instruction Manual
3-27
Input and Output Modules
Rev Jun/05
3.5.12 RTD Input Module
The RTD module is similar in operation to an AI module and uses the same troubleshooting and repair
procedures. The RTD module can accommodate two-wire, three-wire, or four-wire RTDs. If two-wire
RTDs are used, terminals B and C must be connected together. If any of the input wires are broken or
not connected, ROCLINK configuration software indicates the “Raw A/D Input” value is either at
minimum (less than 800) or maximum (greater than 4000) as follows:
♦
An open at terminal A gives a maximum reading.
♦
An open at terminal B gives a minimum reading.
♦
An open at terminal C gives a minimum reading.
To verify the operation of the RTD module:
1.
Disconnect the RTD and connect a jumper between terminals B and C of the RTD module.
2.
Connect an accurate resistor or decade resistance box with a value to give a low end reading
across terminals A and B. The resistance value required can be determined by the temperature-
to-resistance conversion chart for the type of RTD being used.
3.
Use ROCLINK configuration software to verify that the Raw A/D Input value changed and
reflects the Adjusted A/D 0% value.
4.
Change the resistance to reflect a high temperature as determined by the temperature-to-
resistance conversion chart.
5.
Verify that the Raw A/D Input value changed and reflects the Adjusted A/D 100% value.
3.5.13 HART Interface Module
The HART Interface Module provides the source for the HART devices and uses two test procedures to
verify correct operation.
♦
Verify HART Integrity of Loop Power on page 3-27.
♦
Verify HART Communications on page 3-28.
3.5.13.1 Verify HART Integrity of Loop Power
Equipment Required:
Multimeter
1.
Measure voltage between terminals A and B to verify channel 1.
2.
Measure voltage between terminals A and C to verify channel 2.
3.
The voltage read in both measurements should reflect the value of +T less the voltage drop of the
HART devices. Zero voltage indicates an open circuit in the I/O wiring, a defective HART
device, or a defective module.