Model 40 Combustible Gas Indicator

The Model 40 combustible gas indicator (fig. 6-36) has two scales. One scale reads from 0% to 100% of the lower explosive limit. The other scale reads from 0% to 10% of the LEL full scale. A selector switch allows you to quickly change from one scale to the other. Use the following procedures to operate this indicator:

1. Open the cover.

2. Connect the sampling hose required and place the intake end of the hose in fresh air.

3. Turn the selector switch to CHECK.

4. Pull up on the VOLT ADJ knob and turn it all the way over to the left.

5. Pull straight up on the SW knob. The meter pointer should move towards the CHECK position on the scale.

6. Flush the indicator with fresh air. Squeeze the aspirator bulb 10 to 12 times to flush the indicator. Squeeze the aspirator bulb another two times for each 10 feet of sampling hose being used.

7. Adjust the meter pointer to zero. To make this adjustment, pull upon the VOLT ADJ knob and turn it in the direction that the meter pointer needs to go to reach the CHECK position on the scale. The VOLT ADJ knob has to be in the up position to make this adjustment. If you cannot

Figure 6-36.-Combustible Gas Indicator Model 40 (MAF, UDMH vapor). 6-23

get the meter pointer to adjust to the CHECK position of the scale, replace the batteries. Eight D-cell batteries (BA-30) are required to operate the indicator.

8. Turn the SELECTOR switch to the 100% LEL position.

9. Adjust the meter pointer to ZERO. To make this adjustment, pull straight up on the ZERO adjustment knob. Turn the knob so that the meter pointer slightly overshoots ZERO. Then turn the knob slowly in the opposite direction until the meter pointer is on ZERO.

10. Turn the SELECTOR switch to the 10% LEL position.

11. Adjust the meter pointer to ZERO as described in step 9.

12. Turn the SELECTOR switch to 100% LEL.

13. Place the end of the sampling hose in the space being tested.

14. Squeeze the aspirator bulb 10 to 12 times for the indicator and 2 times for each 10 feet of sampling hose being used.

15. If the meter pointer stays below 10 on the lower scale, turn the SELECTOR switch to the 10% LEL position. Continue squeezing the aspirator bulb and take your reading from the top scale.

16. To secure the indicator, flush it and the hose out in fresh air. Then push down the SW knob and shut the cover.