RKI Instruments Inert Gas Testing Eagle with Two Pumps - Manual (Page 60)

54 • Maintenance Eagle Instruction Manual
sensor pins.
10. Install the replacement sensor in reverse order.
11. Set the NULL potentiometer as described below.
NOTE: Allow the instrument to run for 15 minutes before continuing
with these instructions.
12. Calibrate the sensor.
Setting the NULL Potentiometer
When an old CO sensor is replaced, the NULL potentiometer must be
adjusted so that the CO amplifier’s hydrogen compensation will work
properly with the new sensor. The procedure involves applying
hydrogen to the sensor and using the NULL potentiometer to cancel
out the hydrogen response. This adjustment is made only once after
the sensor is replaced and does not need to be made again until the
sensor is replaced again. A concentration of 4,000 ppm or 5,000 ppm
hydrogen is recommended for setting the null. Perform the following
procedure to adjust the NULL pot after changing a sensor.
1. Press and hold the RESET/SILENCE, DISP/ADJ, and LEL/PPM
buttons and then press the POWER/ENTER button. Hold down
all of the buttons until the display reads “ROM No ... .” The
display will then show the mV readout of various test points in the
Eagle circuitry.
2. Unscrew the two large screws on the top of the case, then carefully
lift the top of the case and lay it aside.
3. Locate the NULL potentiometer on the top of the CO amplifier
PCB. The NULL pot is the one closest to the middle of the PCB.
4. Screw the regulator to the H
2
calibration cylinder.
5. Connect the tubing from the regulator to the Eagle probe. Allow 1
minute for the reading to stabilize.
6. Adjust the NULL pot in both directions until you have minimized
the mV reading of testpoint #6 on the Eagle display.
7. Disconnect the tubing from the probe.
8. Unscrew the regulator from the calibration cylinder.
9. Reinstall the top case and tighten the two large screws on the top
of the case.
10. Return to normal operation by pressing on the POWER/ENTER
button.