ST100 Series Flow Meter
TROUBLESHOOTING
Fluid Components International LLC
41
AWG Size
Ohms Per 1000 Feet
14
2.52
15
3.18
16
4.02
17
5.05
18
6.39
19
8.05
20
10.1
21
12.8
22
16.2
23
20.3
24
25.7
Resistance Versus Wire Size (AWG)
Check the Flow Element Voltages
If resistance measurements fail to resolve the problem, or if power cannot be removed from the instrument, measure the following voltages.
Using a DMM set to voltage, make the voltage measurements found in the table below at terminal strip P2A on the flow transmitter or on the
sensor enclosure terminal block. Remote flow element cable resistance will affect the voltage readings at the electronics enclosure.
Wire
Expected Voltage*
HTR EXC to HTR RTN
≈
6.79 VDC
ACT SEN to ACT EXC
≈
0.00 VDC
REF SEN to REF EXC
≈
0.00 VDC
REF EXC to GND
≈
2.20 VDC
ACT EXC to GND
≈
2.21 to 2.82 VDC**
ACT SEN to REF SEN
≈
0.24 VDC**
Approximate Flow Element Voltages at 70 °F
*Voltages vary with temperature, flow rate, and the heater current.
**Voltages vary with the process flow rate.
5. A similar resistance check can be made at the electronics side of the interconnecting cable. The interconnecting cable wires will add
ohmic values depending on the cable wire size and length. The table below can be used to correct flow element measured values
through the interconnecting cable by subtracting the cable resistance from the measured value.
The table values are temperature dependent and may differ several ohms higher or lower depending on the local temperature. The resistance
values shown above are based on an ambient temperature of 70 °F (20 °C). If these resistance values are correct, the remote flow element is
confirmed correct. If the resistance values are not correct there is a problem with the flow element.
