TXP-C20_Instruction_Manual_(Rev1.0)
REV – 1.0
[34-2900-0207-5 ]
24
|
P a g e
gases at the same location. The bridge sensor channel includes bridge amplifier, balance potentiometer, and
adjustable switching regulator for setting the correct sensor excitation voltage. A 3-position coarse gain jumper
allows setting the gain of the bridge amplifier. Bridge sensors not mounted to the TXP-C20 enclosure at the factory
will require the Initial Setup calibration procedure described in section 3.1.4. After performing the one time only
Initial Setup all subsequent calibrations are by the TXP-C20’s electronic Cal Mode menus (see section 2.2.5). Sensors
mounted locally to the TXP-C20 normally do not require Initial Setup since it is performed at the factory.
The electrochemical channel has a preamplifier, bridge amplifier, sensor coefficient jumpers and a 2-position coarse
gain jumper for setting the gain of the bridge amplifier. Socketed resistor R11 controls the gain of the preamplifier
and is installed at the factory (consult factory if sensor gas type is to be changed after shipment). Fault supervision
circuitry forces the TXP-C20 into a FAULT condition upon sensor failure or removal.
The Bridge / EC input option may also be configured to accept 4-20mA inputs for mixing a direct sensor input and a
current loop into the same board. Placing either channel’s 2 position SENSOR/4-20mA jumper (JP4 or JP5) into the
4-20mA position, and installing the associated precision 100 ohm socketed resistor, allows 4-20mA signals to be
applied to the mA+ / mA- terminals (see Optional 4-20mA notes in Figure 4-4). 100-ohm resistors are taped to the
inside of the TXP-C20 enclosure. Bridge amplifiers are bypassed in this configuration. Figure 4-4 shows jumper
options with channel 1 configured for a 4-20mA input and channel 2 for a sensor input.
Figure 4-4 – Optional Bridge / EC Sensor Input Board
4.1.3
Optional Bridge Sensor Input Board
Important!
Dual Bridge Sensor input PCB’s may only be installed into motherboard position P1.
The 10-bit Dual Channel Bridge Sensor Input option shown in Figure 4-5 allows these popular gas detectors to be
connected directly to the TXP-C20 without additional signal conditioning or transmitters. Each channel is equipped
