Galvanic Applied Sciences ProTech903W, Operation Manual

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Revision 1 24 9/10/2019
The sensor block measures the intensity of light reflected off of the sensing tape. The light
emitting diode emits a beam of green light that passes through the rear window and the
rate/read aperture strip and is reflected off of the sensing tape. The reflected light then
passes back through the aperture strip and rear window to reach the photodiode detector,
where it is measured. As the stain on the tape gets darker and darker while exposed to
phosgene, the amount of light reflected back to the photodiode detector is reduced. The
change in the amount of light reflected back to the photodiode detector is directly proportional
to the concentration of phosgene in the sample gas.
The sensor block communicates with the electronics assembly via an RS-485 connection. If
the connection between the sensor block and the electronics assembly is broken for any
reason, a Sensor Communication Alarm will be triggered and the analyzer is considered to be
in a Fail State.
The sensor block contains a temperature sensor that measures the ambient temperature
near the sensor block. This temperature sensor can be used to trigger alarms should the
ambient temperature rise above or drop below set amounts, values that can be set in the
GUI.
The sensor block plays a key role in the tape advance algorithm. While the tape advance
motor is running, the sensor block receives pulses from the pulse counter. When the sensor
block receives the number of pulses set in the GUI it sends a message to the system’s main
processor. The processor then sends a message to the motor to stop advancing the tape.
2.6.4 Compression Head
The compression head is the component in the tape transport system that seals the sensing
tape up against the sample chamber. The compression head is shown in Figure 2-8.
Figure 2-8: Compression Head
The compression head is comprised of a black low-friction plastic held up against the tape
and sample chamber by means of two springs. The low-friction plastic construction ensures
that the tape moves smoothly past the compression head, preventing tape breakage.
The compression head creates a seal between the tape and the sample chamber and it
ensures that the stains on the tape are even and have sharp edges, which produces much
better results. In addition, because the low friction plastic is black, it prevents stray light from
being detected by the photodiode on the sensor block. This in turn prevents inadvertent