Detcon TP-624D - Manual (Page 20)

Model TP-624D
TP-624D Instruction Manual Rev. 0.4 Page 16 of 40
3.3 Normal Operation
In normal operation, the display continuously shows the current sensor reading, which will normally appear as
“0”. Once every minute, the LED display will flash the sensor’s units of measure and the gas type (i.e. ppm
H
2
S). If the sensor is actively experiencing any diagnostic faults, a “Fault Detected” message will scroll across
the display once every minute instead of the units of measure and the gas type. At any time, while the sensor
is in “Fault Detected” mode, PGM1 or PGM2 can be swiped to prompt the sensor to display a list of the active
faults.
In normal operation, the 4-20mA current output linearity corresponds with the full-scale range.
3.4 Calibration Mode (AutoSpan)
Calibration Mode allows for sensor span calibration. Span calibration should be performed on a routine basis
(quarterly minimum) to ensure reliable performance. If a sensor has been exposed to any de-sensitizing gases
or to very high over-range H
2
S levels, then a re-calibration should be considered. Unless otherwise specified,
span adjustment is recommended at 25ppm for the 0-100 and 0-50ppm ranges (and 10ppm for 0-20ppm
range). This function is called “AUTO SPAN.”
Material Requirements:
-Detcon PN 327-000000-000 MicroSafe™ Programming Magnet
-Detcon PN 600-610000-000 Splash Guard with integral Cal Port -OR-
-Detcon PN 943-000006-038 Threaded Calibration Adapter
-Detcon PN 985-241100-321 In-Line Humidifying Tube
-Detcon PN 942-010112-025 H
2
S Span Gas (recommended) or other suitable span gas source containing H
2
S
gas in air balance. A fixed flow rate of 200-500cc/min is recommended.
NOTE 1: Before performing AutoSpan Calibration, verify that the AutoSpan level matches
the span calibration gas concentration as described in Section 3.5.2 Set AutoSpan Level.
NOTE 2: The span gas source must have a normal background concentration of 20.9% O2
(H
2
S balanced with Air). Pure Nitrogen background mixtures are not acceptable! Significant
span calibration inaccuracies will result.
NOTE 3: An H
2
S gas concentration of 25ppm is strongly recommended for 0-50 and 0-
100ppm ranges (10ppm span gas for 0-20ppm range). This should be supplied at a controlled
flow rate of 200 to 500cc/min, with 200cc/min being the recommended flow rate.
Other
concentrations can be used if as they fall within allowable levels.
NOTE 4: Span gas bottles contain 0% humidity and this ultra-low humidity condition will
cause inaccurate readings when used to calibrate a sensor.
To prevent this error, Detcon
prescribes the use of a 24” flexible In-Line Humidifying Tube, which adds the relative
humidity to the span gas. The humidifying tube is not necessary when using a gas generating
calibration device that consists of pumped ambient air and an H
2
S generating source.
CAUTION: Verification that the calibration gas level setting matches the calibration span gas
concentration is required before executing “AutoSpan” calibration. These two numbers must be equal.
AutoSpan consists of entering Calibration Mode and following the menu-displayed instructions. The display
will ask for the application of span gas in a specific concentration. The applied gas concentration must be
equal to the calibration gas level setting.
The factory default setting and recommendation for span gas