Detcon DM-200 - Manual (Page 19)

Model DM-200
DM-200 Instruction Manual Rev. 2.0 Page 15 of 40
Figure 13 Auto Span Sequence - Toxics
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Apply the calibration test gas at a flow rate of 500 milliliters per minute. When the sensor response
exceeds 10% of the applied test gas, the display will change to “Auto Span Test” for a period of 2
minutes.
If sensor response does not exceed 10% of applied gas after 1 minute, the menu “1-Abort Span / 2-Continue
Span” appears. This gives the user an opportunity to verify proper span gas delivery and concentration before
continuing forward. If it is desirable to “Abort Span” and try again, then that choice may be exercised.
At two minutes the message will change to “Auto Span Adjust” for an additional 30 seconds. During this
period the sensor will analyze the signal for stability. The criterion for stability is signal drift within ±2% of
full scale in 30 seconds. If met, the message changes to “Auto Span Complete”.
If not met, up to 4 additional 30 second stability check periods are administered. If all 5 stability checks fail,
then the unit returns to Normal Operations with the original Auto Span parameter intact. An alternating
message of “Span Calibration Fault” is displayed to remind the user that a re-calibration is still necessary.
With “Auto Span Complete” achieved, the display now reports the remaining “Sensor Life xx%”, then the
“New Span Date”, and then “Remove Span Gas / xx PPM” which prompts the user to remove the span gas
from the sensor. During “Remove Span Gas / xx PPM”, the sensor recovers toward zero, and when the
signal level falls below 10% of full scale the display changes to “Return to Normal Operation”.
Additional Notes
1. Upon entering the calibration menu, the 4-20 mA signal drops to 3.5 mA and is held at this level until
the unit returns to normal operation.