Fluid Components International 8-66B_12-64B Series Manual Troubleshooting - Manual (Page 2)

FLUID COMPONENTS INTL CHAPTER 5 - TROUBLESHOOTING
Models 12-64/8-66 Basic Switch 5 - 2 Doc. No. 06EN003264 Rev. A
1. Review the application design with plant operation personnel and plant engineers.
2. Ensure that plant equipment such as pressure and temperature instruments conform to the actual conditions.
3. Verify operating temperature, operating pressure, line size, and gas medium.
Verification of Sensing Element Resistance
The measurements are based on a standard (5K ohm RTD at 70°F, or 21°C) sensing element. Variation of ± 100
ohms from nominal is to be expected, depending on temperature. The maximum allowable difference in resistance
between matched RTD's is 1% at ambient temperature (immersed in water). The heater resistance should be 225
±5
ohms. Be sure to subtract the cable resistance to get the true resistance.
1. Turn off the operating power to the instrument.
2. Gently remove (pull straight out) the control circuit from the socket. Using a DMM, measure the resistance of
the active and reference RTD sensing elements and the heater as found in Table 5-1 to determine if the sensing
element is functional.
Note: The resistance of the active RTD will be greater than the resistance of the reference RTD whenever the
heater is on.
If there is an indication of an open or short in the RTD, the sensing element will need to be replaced.
After replacing the sensing element, it will be necessary to follow the alarm set point adjustment procedures found in
the Operation Chapter before returning the instrument to service.
If the sensing element resistance is correct, proceed to the voltage verification test.
Table 5-1. Sensing Element Resistances In Ohms
*Resistance varies with temperature. These values should be ± 5 ohms at 70 ° F (21 ° C).
Verification of Sensing Element Voltage
If the above resistance checks are good, plug in the control circuit and apply power. Measure the voltages in
Table 5-2. If the voltages are not correct, then remove and replace the control circuit.
Table 5-2. Sensing Element Voltages
From Terminal Pin To Terminal Pin Voltage Expected**
9 (+) 7 (-) 22VDC
7 (+) 8 (-) 12VDC
9 (+) 8 (-) 10VDC
10 (+) 7 (-) 19VDC
**Voltages are dependent on temperature.
From Terminal (Pin) To Terminal (Pin) Expected Ohms*
Heater (7) Heater (10) 225
Ref Sen (9) Com Sen (8) 5000
Ref Sen (9) Act Sen (7) 10000
Act Sen (7) Com Sen (8) 5000