Fluid Components International MT91 Manual Troubleshooting - Manual (Page 4)

FLUID COMPONENTS INTL CHAPTER 5 - TROUBLESHOOTING
Model MT91 Multipoint Flowmeter 5 - 4 Doc. No. 003185 Rev. B
Pin Number Approximate Resistance
2 to 3 1000 ohms
2 to 4 1000 ohms
2 to 5 1000 ohms
2 to 6 1000 ohms
7 to 8 220 ohms
3 to 5 0 ohms
4 to 6 0 ohms
Check the Resistance of the Sensing Points
To simplify the discussion below, the nomenclature J1 and TB1-HD1 will be used to represent all individual
sensing points.
Use Table 5-2 to determine if the flow element is wired incorrectly or has failed. Turn off the input power to the
flow transmitter. Disconnect the suspect sensing point’s connector from the remote enclosure. Measure
resistances at the points shown in Table 5-2 by touching the DMM test leads to the connector terminal screws. See
Figure 5-1. (Plug the connector back in when finished.)
Note: All resistances referred to below are for standard instruments using 1000 ohms RTDs. For high
temperature units, replace 1000 ohms with 100 ohms.
All resistances in Table 5-2 are based on a temperature of 32°F (0°C). Expect reading to be higher at room
temperature, approximately 1080 ohms
for a standard instrument or 110 ohms for a high temperature instrument.
For a closer estimation, use the following equation:
Ra = Ri x [1 + (0.00385 x T)]
Ri = initial resistance ( 100 ohms for high temperature flowmeters, 1000 ohms for standard temperature
flowmeters)
Ra = actual resistance
T = degrees Celsius
The numbers in Figure 5-1 have been added to the wire designations for discussion purposes and are not found on
the connector plugs or wires.
If the measured resistances correspond to Table 5-2, then the sensing point is sound. The problem lies else where.
Skip the rest of this section and proceed with the next section, Analog Output Test.
If the measured values do not correspond to Table 5-2, then a problem exists in the flow element or the cable.
Wires within the cable could be shorted or open. To isolate a problem with the cable, check the sensing point
resistances of the corresponding terminal connector located within the flow element enclosure. Measure
resistances at the points shown in Table 5-3 by touching the DMM test leads to the terminal screws. See Figure 5-
1.
If the values do not correspond with Table 5-3, remove the cable wires from the terminal connector and measure
resistances again. The measured resistances should correspond approximately to the values in Table 5-3.
Figure 5-1. J1 Connector Plug on the
Backplane Board
Table 5-2. Resistances at J1 Connector Plug
on the Backplane Board