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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.

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Emerson ROC364 Bedienerhandbuch Seite 61