Analytical-industries GPR-1600 MS Series PPB Oxygen Analyzer Manuale Utente Scaricare il pdf (Pagina 48)

Advanced Instruments Inc.

Appendix B

Correlating Readings - LCD Display and 4-20mA Output

In rare instances the 4-20mA 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 4mA signal output to correlate with the reading displayed by the LCD.

For optimum accuracy make two separate adjustments as follows:

1. OUTPUT ZERO feature: To adjust the 4mA signal output and requires zero gas.

2. OUTPUT SPAN feature: To adjust the 20mA signal output and requires span gas near full range.

In the field or in the absence of the preferred gases, use the OUTPUT SPAN feature and adjust the 20mA signal output using

the span gas available.

Procedure – regardless of type of adjustment:

1. The microprocessor defaults to 100% to start.

2. The “actual” 4-20mA signal output will be adjusted to the “theoretical” value of the LCD display.

3. Adjustment general rule:

a) If the actual 4-20mA value < the theoretical LCD value, the adjustment value will be > 100%.

b) If the actual 4-20mA value > the theoretical LCD value, the adjustment value will be < 100%.

4. Convert the “actual” reading of the LCD display to the “theoretical” 4-20mA as follows:

a) Divide the “actual” (ppm or percent) LCD reading by the value of the span gas available.

b) Multiply 16mA (20mA – 4mA) times the “result of a.”

c) Add 4mA plus the “result of b.” to obtain the “theoretical” 4-20mA signal output value.

5. Adjustment value: Divide the theoretical by the actual 4-20mA values and multiply by 100.

6. Enter the adjustment value via OUTPUT ZERO or OUTPUT SPAN routines described below.

Example: Analyzer reading is 60 ppm oxygen (100 ppm range) on 84 ppm span gas, 4-20mA signal output at PLC is 24mA

Solution: a) Use OUTPUT SPAN feature to make the adjustment.

b) Adjustment will be < 100% (default value of OUTPUT SPAN feature).

c) 13.6mA is the “theoretical” 4-20mA converted from the “actual” reading of the LCD.

60 ppm divided by 84 ppm = 0.71 or 71%

16mA multiplied by 0.71 = 11.36mA

4mA plus 11.36mA = 15.36mA “theoretical” 4-20mA signal output value

d) 15.36mA divided by 24mA the “actual” 4-20mA value = 64.0 adjustment value

e) Enter 64.0 via OUTPUT SPAN procedure below.

Output Zero

7. Access the MAIN MENU by pressing the MENU key.

8. Advance the reverse shade cursor using the ARROW keys to highlight CALIBRATION.

9. Press the ENTER key to select the highlighted menu option.

10. The following displays appear:

MAIN MENU

AUTO SAMPLE

MANUAL SAMPLE

CALIBRATION

>>>

CALIBRATION

SPAN CALIBRATE

ZERO CALIBRATE

DEFAULT SPAN

DEFAULT ZERO

OUTPUT SPAN

OUTPUT ZERO

11. Advance the reverse shade cursor using the ARROW keys to highlight DEFAULT ZERO.

12. Press the ENTER key to select the highlighted menu option.

13. The following display appears:

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Analytical-industries GPR-1600 MS Series PPB Oxygen Analyzer Manuale Utente Pagina 48

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