Detcon DM-200 - Manual (Page 13)

Model DM-200
DM-200 Instruction Manual Rev. 2.0 Page 9 of 40
2.8 Start Up
Upon completion of all mechanical mounting and termination of all field wiring, apply system power and
observe the following normal condition:
A temporary upscale reading will occur as the sensor powers up. This upscale reading should clear to 0ppm
within approximately 30 minutes of turn-on, assuming there is no gas in the area of the sensor.
NOTE: If the display contrast needs adjustment, refer to Section 4.3 Display Contrast Adjust
Zero Clearing with Biased Cells
Some electrochemical sensors are biased with an excitation voltage. When power to the sensor is lost, this
bias voltage slowly decays. When power is restored after long periods of time (multiple hours), a surge in
sensor output takes place and a long and slow re-establishing of the sensor’s zero baseline takes place. This
re-stabilization time may range from 1 hour to 24 hours depending on the type of sensor and range of
operation. The sensor types that this applies to are the following: HCl, NO, NH3 (DM-202-NH3), plus all the
VOC sensors, C2H30, C2H2, C3H3N, C4H6, CS2, COS, C2H6S, C3H5OCL, C2H5OH, C2H4, C2H4O,
CH2O, CH3OH, C4H4S, C4H6O2, C6H5CH3 and C2H3CL.
If this characteristic is problematic for your specific application, a battery backup or uninterruptible power
supply is recommended.
2.9 Initial Operational Tests
After a warm up period has been allowed for, the sensor should be checked to verify sensitivity to its target
gas.
Material Requirements
*
Span gas containing the target gas in air or nitrogen. It is recommended that the target gas
concentration be 50% of scale at a controlled flow rate of 500 ml/min. For example, a Model DM-
200-H2S UniTox™ sensor in the range 0-100ppm would require a test gas of 50ppm H2S. For a
sensor with a range of 0-10ppm a test gas of 5ppm is recommended, etc.
For oxygen, use test gas containing 100% nitrogen.
a)
Attach tubing to the center port connection of Splashguard. Apply the test gas at a controlled flow rate
of 500ml/m. Observe that the LCD display increases to a level of 20% of range or higher. For oxygen,
observe that the display decreases to a level of 3% or less.
b) Remove the test gas and observe that the LCD display decreases to “0 PPM”. For oxygen, observe
that the LCD display increases back close to 20.9%.
Initial operational tests are complete. Detcon toxic gas sensors are pre-calibrated prior to shipment and in
most cases will not require significant adjustment on start up. However, it is recommended that a complete
calibration test and adjustment be performed within 24 hours of installation. Refer to calibration instructions
in later text.