TROUBLESHOOTING
ST100 Series Flow Meter
44
Fluid Components International LLC
Allowable Limits
Example 1 - 4-20 mA output check using 1-5 VDC measurement.
Accuracy: ±(0.75% r 0.5% full scale) from GF90 Manual
Sample 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.
