Analytical Industries GPR-1800 AIS ATEX Trace PPM Oxygen Analyzer - Manual (Page 39)

Advanced Instruments Inc.
39
Appendix B
Correlating Readings – LCD Display and 4-20mA or 0-1V Signal Outputs
In rare instances the signal output may not agree to the reading displayed by the LCD. The OUTPUT ZERO and OUTPUT SPAN
features enable the user to adjust the signal output to correlate with the LCD reading.
For optimum accuracy make two separate adjustments as follows:
1. OUTPUT ZERO feature: To adjust the 4mA or 0V signal output and requires zero gas.
2. OUTPUT SPAN feature: To adjust the 20mA or 1V signal output and requires span gas near full range.
Note: In the field or in the absence of the preferred gases, use the OUTPUT SPAN feature and adjust the 20mA or 1V signal
output using the span gas available.
Guideline:
If the actual signal output value < the theoretical LCD value, the adjustment value will be < 100%.
If the actual signal output value > the theoretical LCD value, the adjustment value will be > 100%.
Procedure – regardless of type of adjustment – with examples: Signal Output
4-20mA 0-1V
1) The OUTPUT ZERO and OUTPUT SPAN default values . . . 100.0% 100.0%
2) Adjust the “actual signal output” . . . 24mA 1.2V
to the “theoretical signal output ” based on the “span gas value” of . . . 84 ppm span gas 84% span gas
3) and the “actual LCD reading” . . . 60 ppm 80%
a) “actual LCD reading” divided by the “span gas value” 60 / 84 = .71 80 / 84 = .95
b) 16mA (20mA less 4mA) multiplied by the result in 3a) .71 x 16 = 11.36 NA
c) 4mA plus the result of 3b) = “theoretical signal output” 4 + 11.36 = 15.36mA .95V (from a)
4) “Adjustment Value” = (“theoretical” divided by “actual signal output “) x 100 (15.36 / 24) x 100 = 64 (.95 / 1.2) x 100 = 79
5) Proof = (“actual signal output” multiplied by “adjustment value”) divided by 100 (24 x 64) / 100 = 15.36mA (1.2 x 79) / 100 = .95V
6) ENTER “adjustment value” via OUTPUT ZERO or OUTPUT SPAN routines below. 64 79
7) Fine tuning . . . after checking the new “actual signal output” at the PLC 19.5mA .98V
8) Repeat Step #4 and substitute the latest “actual signal output” (15.36 / 19.5) x 100 =78.8 (.95 / .98) x 100 = 96.9
9) Proof = (“actual signal output” multiplied by “adjustment value”) divided by 100 (19.5 x 78.8) / 100 = 15.36 (.98 x 96.9) / 100 = 95
10) ENTER “adjustment value” via OUTPUT ZERO or OUTPUT SPAN routines below. 75 95