FCI MT100 - Heater Current Check; Allowable Limits; Table 28 - Heater Current

TROUBLESHOOTING MT100 Multipoint Flow Meter
Heater Current Check
The heater current can be checked at TP1 on the FES-200. Set the DMM to DC volts (V).
1. Connect the positive lead of the DMM to TP1 on the FES-200.
2. Connect the negative lead of the DMM to the HTR EXC terminal of the flow transmitter.
The measured mV value of heater current will be 10x larger than the actual mA heater current. For example, 750 mV indicates 75 mA
heater current. The measured value of heater current must be within ±0.15 mA of the factory set value. See Table 28 below.
Table 28 – Heater Current
FCI Transmitter Model
Factory-set Heater Current
DMM Reading
MT100S, S-type sensor probe
90 mA
900 mV
MT100S, F-type sensor probe
MT100M, mast style probe
75 mA 750 mV
Allowable Limits
Example 1 - 4-20 mA output check using 1-5 VDC measurement.
Accuracy: ±(0.75% reading + 0.5% full scale) from GF90 Manual
Example Delta R Table entry:
Delta R (ohms)
VDC Across
250 ohms
mA Output
Unit dR
Indicated
Display
71.08 2.995 11.98 71.197 154.8 SCFM
• Measure VDC with FES-200 thumbwheel set to 071.08 = 3.011 VDC measured on DMM.
•
Determine allowable VDC limits for the 2.995 VDC table value:
Note:
Since the 1-5 VDC range starts at 1 VDC, account for this offset by subtracting 1 VDC from both the “reading” of
2.995 VDC and the “full scale” of 5 VDC.
• Allowable VDC limits = 0.0075 x (2.995 – 1) + 0.005 x (5 – 1) = ±0.035 VDC
The measured value of 3.011 VDC is within the allowable limits of 2.995 ±0.035 VDC.
Example 2 - 4-20 mA output check (using example 1 sample data)
• Measure mA with FES-200 thumbwheel set to 071.08 = 12.04 mA measured on DMM.
• Determine allowable mA limits for the 11.98 mA table value:
Note:
Since the 4-20 mA range starts at 4 mA, account for this offset by subtracting 4 mA from both the “reading” of 11.98
mA and the “full scale” of 20 mA.
• Allowable mA limits = 0.0075 x (11.98 – 4) + 0.005 x (20 – 4) = ±0.139 mA
The measured value of 12.04 mA is within the allowable limits of 11.98 ±0.139 mA.
Example 3 - Indicated Display Check (using information from above examples)
• Record the indicated display value with FES-200 thumbwheel set to 071.08 = 156 SCFM indicated on display.
•
Determine allowable limits for the 154.8 SCFM table value:
Note:
The full scale display value is 310 SCFM in this example.
• Allowable Indicated flow limits = 0.0075 x 154.8 SCFM + 0.005 x 310 SCFM = ± 2.71 SCFM
The indicated value of 156 SCFM is within the allowable limits of 154.8 ±2.71 SCFM.
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