Optional *Bridge Sensor Input Board; Catalytic Bead Sensor Initial Setup - Honeywell HA71 Technical Manual

HA71 Digital Gas Controller

3.1.3 Optional *Bridge Sensor Input Board

An optional 8-channel, 12 bit Bridge Sensor Input board allows these
popular gas detectors to be connected directly to the HA71 without
additional signal conditioning or transmitters. Up to four dual channel
10-0192 modules may be installed in each 8-channel 10-0191. Each
10-0192 channel is equipped with a bridge amplifier and balance
potentiometer and an adjustable switching regulator for setting the
correct sensor excitation voltage. A 3 position coarse gain jumper
allows setting the gain of the bridge amplifier. Fault supervision
circuitry forces the HA71 into a FAULT condition upon sensor failure
or removal.
This option may also be configured to accept 4-20mA inputs for mixing
bridge sensors and current loops into the same board. Placing any
channel's 2 position LEL/4-20mA jumper into 4-20mA position and
installing the associated precision 100 ohm socketed resistor allows
4-20mA signals to be applied to it's C and A terminals. The 10-0192
sensor modules are not required for channels accepting 4-20mA.
Channels receiving input data from this board should have the Data
From: menu set for Sensor, as described in
activates Cal Mode menus described in
zero and span sensor readings. After performing the one time only
Initial Setup as described below, all subsequent calibrations are by
the HA71's electronic Cal Mode menus.
*Catalytic sensors connected directly to the HA71 should be limited
to ranges of 0-1000ppm.

3.1.4 Catalytic Bead Sensor Initial Setup

Catalytic bead sensors vary widely in power requirements and
sensitivity. It is therefore important to configure each channel to match
the sensor with which it will operate.
1. Prior to connecting sensors, apply power to the system.
HA71 Technical Manual
Section 2.2.4. This
Section 2.2.13 needed to
3-5
Note
This PCB requires 24VDC power be connected to its TB2
terminals 1 and 2 as shown in Figure 3-5. Suitable fused power
is available from the Main I/O board's TB2 terminal 10 & 12
(see Figure 3-1). Measure the voltage between each channel's
A and R terminals and set the Voltage Adjust potentiometers
for the correct sensor excitation voltage. This may range from
1.5 volts to 7.5 volts depending upon sensor specifications.
CAutIoN
Sensors may be damaged by accidental over voltage conditions. It is
recommended the Voltage Adjust potentiometer screws be covered by
a dollop of RTV or similar material after completion of this procedure
to avoid accidental over voltage conditions.
2. Remove system power and connect sensor wires to the R-C-A
terminals. Reapply system power and confirm correct voltage
across each sensor's A and R terminals.
Note
If sensor wires are long, it may be necessary to measure the
excitation voltage at the sensor end to compensate for I
losses in the wiring.
3. With the minus voltmeter lead on TB2-2 (common), connect the
plus lead to the channel's test point. With zero air on that sensor,
adjust it's Balance potentiometer for .4 volts at the test point.
4. Apply 50% LEL combustible span gas to the sensor and allow
the test point voltage to stabilize. Two volts = 100% input to the
A – D Converter and .4 volts = 0%. Therefore, 1.2 volts = 50%.
Place the 3 position Coarse LEL Gain jumper into the position
which reads between .8 volts and 1.2 volts on the test point
with 50% LEL gas on the sensor. Gain settings for each jumper
position are as follows: no jumper = 1, LOW = 7, MED = 21, HI
R
2
Revision 3 (04/08)