Detcon DM-400IS - Manual (Page 19)

RANGE RANGE RANGE RANGE
PPM 0-10ppm 0-25ppm 0-50ppm 0-100ppm
0 40 mV 40 mV 40 mV 40 mV
1 56 mV 46.4 mV 43.2 mV 41.6 mV
5 120 mV 72 mV 56 mV 48 mV
10 200 mV 104 mV 72 mV 56 mV
25 – 200 mV 120 mV 80 mV
50 – – 200 mV 120 mV
100 – – – 200 mV
If calibration is being done with a gas concentration other than 50% of scale, you can determine the proper signal volt-
age by dividing 160 mV by the range of detection and then multiplying that f igure by the concentration of gas. For
example, if you are calibrating a sensor with a range of 0-100ppm with a gas standard that contains 10ppm, you would
divide 160 (mV) by 100 (ppm) and then multiply that f igure by 10 (ppm). Then add the base line of 40 (mV) to arrive
at the proper signal voltage of 56 mV.
3.6.4 Calibration Frequency
In most applications, monthly to quarterly calibration intervals will assure reliable detection. However, industrial envi-
ronments differ. Upon initial installation and commissioning, close frequency tests should be performed, weekly to
monthly. Records should be kept. Less frequent test schedules should be implemented based on analysis of tests prior
to adjustment.
3.7 T
ROUBLE
S
HOOTING
Sensor reads Over-range after Power-up
Probable Cause: Biased sensor requiring additional stabilization time.
1. Verify if this is a Biased sensor (see section 3.5).
2. Wait up to 8 hours for unit to come on-scale if using a low range biased sensor.
3. Verify that there is not large amounts of target gas or interfering gases in background.
Reading Higher than Anticipated
Probable Causes: Target or Interfering gases in background, Incorrect calibration for Zero or Span, Biased sensor still
stabilizing.
1. Verify no target or interfering gases are present.
2. Redo Zero and Span calibrations with validated Zero Gas and Span Gas standards.
3. If recovering after a start-up, give more time to stabilize.
Reading Lower than Anticipated
Probable Causes: Target gas or Interfering gases in background during Zero Calibration, Zero Calibration done before
unit f inished stabilizing, Incorrect Span Calibration.
1. Redo Zero and Span calibrations with validated Zero Gas and Span Gas standards.
Cannot Zero Calibrate to 40 mV
Probable Causes: Target gas or Interfering gases in background during Zero Calibration, Failed electrochemical sensor.
1. Verify no target or interfering gases are present.
2. Redo Zero and Span calibrations with validated Zero Gas and Span Gas standards.
3. If recovering after a start-up, give more time to stabilize.
Cannot do Span Calibration (not enough adjustment in span pots)
Probable Causes: Failed electrochemical sensor, ice/mud/dust blocking sensor membrane, invalid span calibration gas
do to age and contamination or insuff icient f low rate.
1. Verify there is no ice/mud/dust blocking sensor membrane.
2. Redo Span Calibration with validated Span Gas standard (check with Pull Tube).
3. Replace with new electrochemical sensor.
DM-400IS Toxic Gas Sensors PG.19