RKI Instruments NP-204 User Manual
Page 12
NP-204
RKI Instruments, Inc.
High Range sensor
Replace the high range sensor filaments when:
1 .
The High range cannot be calibrated correctly.
2 .
The high range cannot be set to zero after warmup using the internal ZERO (H)
potentiometer.
Sensor Replacement
1 .
Take the NP-204 to a non-hazardous location and turn the power off.
2 .
Remove the instrument from the carrying case.
3 .
Loosen the two large screws on the top face of the instrument, lift the top half of
the case away from the bottom case, and lay the top case upside down on the
workbench.
4 .
Locate the sensor/chamber block assembly. It is a rectangular shaped block in
the case corner right next to the inlet fitting. The sensor filament sets are each
held in place by a U shaped bracket and two screws. Filament sets have colored
wires soldered to their rear posts, and these wires are connected to screw
terminals on the circuit board.
5 .
To replace individual sensors, proceed as follows:
Low range sensor
A.
The low range sensor has wire colors of Black, Red, and White. Loosen
(but do not remove) the screws on the circuit board holding these
wires (terminals T1, T2, and T3) and remove the wires.
B.
Remove the two screws holding the U shaped bracket which secures
the Low range sensor filaments into the sample chamber. Remove the
bracket and pull the sensor filaments from the chamber.
C.
Install the replacement filaments into the chamber. Insure that the
filaments with the black and white wires are installed into the hole
closest to the corner of the instrument. Replace the U shaped bracket
and tighten its two screws securely.
D.
Attach the three wires to the terminals on the circuit board, and
tighten the screw terminals securely. Insure that the color coded
wires go to the proper terminals, as indicated by the color wording
printed on the circuit board.
E.
After sensor replacement, the instrument must be calibrated on a
known gas sample. Refer to the calibration section of this manual for
calibration instructions.
High range sensor
A.
The High range sensor has wire colors of Yellow, Blue, and Red.
Loosen ( but do not remove) the screws on the circuit board holding
these wires (terminals T4, T5, and T6) and remove the wires.
Page 12 of 13
version 65.1