AMC-400 Series Digital Transmitter with Smart Sensor 2
15
16.SS2 Male Connector:
This 7 pin connector mates with the Digital Transmitter
female connector. This connector carries the power and
communication.
17.VDD Test Point:
This VDD Test Point is to be used by service technicians
only. It is the Smart Sensor 2 control logic supply voltage
and must be 3.45+/-5% Volts DC.
18.GND Test Point:
This GND Test Point is to be used by service technicians
only with appropriate instrumentation such as a voltmeter. It
is the signal reference point for the Smart Sensor 2 control
logic.
19.VREF Test Point:
This VREF Test Point is to be used by service technicians
only. It must be 1.8 Volts DC.
20.Sensor:
This component is a 3 pin Catalytic sensor. This component
is permanently fastened to the Smart Sensor 2 Module.
21.SIG Test Point:
This Sig Test Point is to be used by service technicians only
with appropriate instrumentation such as a voltmeter. It is
the amplified sensor output as seen by the analog to digital
converter. Under normal operation zero gas situation it
tracks the 1.8 +/- 0.4 Volts DC VREF. When a combustible
gas is applied this SIG Test Point increases toward 3.45
Volts DC.
3.6 CATALYTIC SENSOR CHARACTERISTICS
3.6.1 CONTAMINANTS
The performance of the catalytic combustion type gas sensors may be affected by exposure to
substances known as poisons and inhibitors. Inhibitors are present in volatile substances
containing halogens or sulphur compounds. Sensors may recover their sensitivity
characteristics after exposure to inhibitors has ceased. Some substances produce a permanent
poisoning effect on the catalyst. These poisons include silicone oils, greases and petroleum
additives such as tetraethyl lead and phosphate esters. Always be cautious of by products that
may evolve from the thermal decomposition of materials such as plastics.
3.6.2 CROSS
SENSITIVITY
The catalytic sensor is also sensitive to other combustible gases. See Table 3-1. As a result the
sensor will provide protection for some of these gases as well.
