Det-Tronics THZ HART Combustible Gas Transmitter - Manual (Page 5)

Important Calibration Notes
• Ensure that the transmitter is properly programmed
for the gas concentration being used for calibration.
• Ensure that only clean air is present at the sensor
prior to entering the calibration mode. If the possi-
bility of background gases exists, purge the sensor
with clean air to ensure accurate calibration.
• Ensure that the concentration of the calibration gas
matches the calibration gas setting. Typically, cali-
bration gas concentration equal to 50% full scale is
used.
• Inspect the sensor. Loss of sensitivity can be
caused by various factors. One common cause is
by clogging of the hydrophobic or sintered filters by
dirt, oil, paint, etc. If the filter is dirty or plugged, it
should be replaced.
• When calibrating a C7065E O2 Sensor, the initial
“zero” calibration requires activation of a switch
located inside the sensor housing. Subsequent cal-
ibrations of the sensor do not require switch activa-
tion. Always calibrate the sensor using 20.9% O2 if
ambient air is less than 20.9% O2.
CALIBRATION PROCEDURE
The DEC-THZ gas detector is calibrated using the
HART communication menu's "Sensor Trim" function.
The Sensor Trim function is found in the HART online
menu, under the Device Setup selection within the
Diagnostics & Service menu selection. Be sure to
select the "user trim" mode and the "two-point" trim
option. After selecting the 2-point sensor trim com-
mand, it is critical that the values "200" and "600" be
entered for the corresponding low and high trim
points. When the HART menu instructs the operator
to enter the low (1) trim point signal, simply ensure
that the sensor is exposed to clean air, which will
result in a 4 ma signal output level, and then enter the
low (1) trim command. When the HART menu
instructs the operator to enter the high (2) trim point
signal, the operator should apply 50% full scale cali-
bration gas to the sensor for approximately 60 sec-
onds, and then enter the high (2) trim point command.
After the two trim points have been set and adjusted,
the calibration is complete.
DEC-THZ calibration can be conducted using a HART
HC275 communicator, a PC using a HART modem
and the DEC-THZ configuration program, or a HART
compatible system such as the Emerson Asset
Manager System.
For additional information and guidance, please refer
to specific instruction manuals or contact Detector
Electronics Corporation Product Marketing depart-
ment.
5 95-8550