Detcon DM-400IS - Manual (Page 17)

3.5 S TART U P
Upon completion of all mechanical mounting and termination of all f ield wiring, apply system power and observe the
following normal condition:
a) Detcon electronic controller “Fault” LED is off.
b) A temporary upscale reading will occur as the sensor powers up. This upscale reading should clear to “0” ppm with-
in approximately 30 minutes of turn-on, assuming there is no gas in the area of the sensor.
NOTE: 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 (multiple hours) of being unpowered, 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 (DM402IS-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 specif ic application, a battery backup or uninterruptible power supply is rec-
ommended.
3.5.1 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
* Digital volt meter
* Jewelers type screwdriver
* Detcon PN 943-000217-5A1 Calibration Adapter
* 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 f low rate of 500 ml/min. For example, a Model DM-400IS-H2S 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.
a) Remove the junction box cover.
b) Measure the voltage between signal test points: zero gas conditions should provide a reading of between 39 and 40
mV DC. If necessary, adjust the zero potentiometer to achieve this reading.
c) Attach the calibration adapter to the sensor housing. Apply the test gas at a controlled flow rate of 500 ml/m. Observe
that the signal voltage increases to a level of 80 mV DC or higher.
d) Remove the test gas and observe that the signal decreases to between 39 and 40 mV DC.
Initial operational tests are complete. Detcon Model series DM-400IS sensors are pre-calibrated prior to shipment and
will, in most cases, not require signif icant adjustment on start up. However, Detcon recommends that a complete cali-
bration test and adjustment be performed within 24 hours of installation. Refer to calibration instructions in later text.
3.6 C
ALIBRATION
Note: Calibration gas mixtures of the target gas in air or nitrogen are acceptable.
3.6.1 Material Requirements
* Digital volt meter
* Jewelers type screwdriver
* Detcon PN 943-000217-5A1 Calibration Adapter
* Span Gas containing the target gas in air or nitrogen.
NOTE 1: It is recommended that the target gas concentration be 50% of scale to assure optimum linearity. For
example, Model DM-400IS-H2S 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 would be recommended, etc. If a test gas will be used that has a con-
centration other than 50% of scale, see the additional instructions for determining the proper signal voltage in sec-
tion 3.6.3 (Calibration Notes) below. To determine the gas and range of the sensor, refer to the sensor face plate
and/or external labeling.
DM-400IS Toxic Gas Sensors PG.17