iWorX GA-200 Series, GA-200A, GA-200B Technical Note

GA-200 Gas Analyzer

Technical

Note

GA-200 Gas Analyzer

Overview

The GA-200 Gas Analyzer uses sensors to measure and display the
concentrations of oxygen and carbon dioxide in a sample as the percentage of a
gas in the sample by volume. This method of expressing the concentration of a gas
in a sample is also known as the percent volume fraction. In addition to the
sampling and sensing systems in the GA-200, the unit has a fluorescent display
used for observing measurements and analog outputs that allow the unit to be
connected to iWorx data recorders.

When measuring the concentrations of oxygen and carbon dioxide in a gas, a
sample is pumped from the input port on the front panel of the GA-200, through the
sample cell, and out an exhaust port on the back of the unit. Gas samples are
drawn into the unit through an external filter on the input port that protects the
sensors from contamination and through Nafion tubing connected to the filter that
removes moisture from the samples that would affect the measurements and the
unit's calibration.

The GA-200 Gas Analyzer has the ability to measure and record both oxygen and
carbon dioxide concentrations over the ranges normally recorded from human and
animal subjects.

Front Panel

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GA-200 Front Panel

GA-200 Gas Analyzer

The front panel of the GA-200 (both A and B) has a keypad, a display used to
program the modes and parameters of the unit, and an inlet port for the gas
sample. For use with LabScribe and iWorx data recorders, it is not necessary to do
any programming through the keypad. All parameters are set in the software, as
described below.

Rear Panel: GA-200A

GA-200A Rear Panel

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The rear panel of the GA-200A has the following features: a switch, a power input,
an RS-232 serial port for connection to a computer, an oxygen sensor output, and
a gas outlet. The output of the carbon dioxide sensor is incorporated into the relay
terminal which allows the unit to be connected to other devices.

1) Power for the GA-200A is supplied by an external power supply. The power
supply is connected to the unit through the connector labeled 12V, 1.5A. Press
the side of the power switch labeled I to turn on the GA-200A. Press O on the
switch when it is time to turn the unit off.

2) The GA-200A can be interfaced to a computer through a serial (RS-232) data
stream. The default data format is 9600 baud, 8 bit, and no parity with
alternate baud rates of 2400, 4800, 19200, and 38400. The signals present are
RXD, TXD, and ground through the 9-pin D connector on the back panel of the
unit.

3) The signal from the oxygen sensor can be recorded from the BNC output
labeled OXYGEN SENSOR, 0-1V = 0-100%. The amplitude of the signal
ranges from 0 to 1 Volt DC which corresponds to a range of 0 to 100% oxygen,
or 1mV for each 0.01% oxygen. The ground of this output is common to the
instrument case and the power supply.

4) The exhaust port of the sampling circuit is labeled OUTLET. A scavenging

system can be connected to this port to collect any gases passing through the
GA-200A.

5) Several relays are available from the terminal block on the rear panel of the

GA-200A. These relays are normally open, but close when the oxygen sensor
detects various alarm conditions. For DC loads, these relays are rated from 5
Amps at 30 Volts DC to 0.25 Amps at 300 Volts DC in an open circuit. For AC
loads, these relays are rated from 5 Amps at 250 Volts. When the sockets are

GA-200 Gas Analyzer

numbered from left to right:

• Sockets 1 (Common), 2 (NC), and 3 (NO) are the connections for Limit

Relay A.

• Sockets 4 (Common), 5 (NC), and 6 (NO) are for Limit Relay B.

• Sockets 7 (Common), 8 (NC), and 9 (NO) are for Warning Relay.

• Sockets 10 (Common), 11 (NC), and 12 (NO) are for System OK.

6) An analog output for the carbon dioxide sensor and an additional analog output
for the oxygen sensor are available from the terminal block. These outputs are
non-isolated current sources that are referenced to the current output ground.
The range of each current output is 4 to 20 mA and a maximum output voltage
of 10 Volts. The oxygen and carbon dioxide concentrations that are equal to the
outputs at 4 mA and 20 mA are normally set to the low and high limits of the
sensitivity ranges of the two gases, respectively: For example, the 4 mA current
output of the oxygen sensor is set to 0%, and the 20 mA current output is set to
100%.

• Socket 13 is the Ground for the both current outputs.

• Socket 14 is the oxygen current output.

• Socket 15 is the carbon dioxide current output.

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GA-200B: Rear Panel

GA-200B Rear Panel

The rear panel of the GA-200B has the following features: a switch, a power input,
an RS-232 serial port for direct connection to a computer, an oxygen sensor
output, a carbon dioxide sensor output, and a gas outlet.

1) Power for the GA-200B is supplied by an external power supply. The power
supply is connected to the unit through the connector labeled 12V, 1.5A. Press
the side of the power switch labeled I to turn on the GA-200B. Press O on the
switch when it is time to turn the unit off.

2) The GA-200B can be interfaced to a computer through a serial (RS-232) data
stream. The default data format is 9600 baud, 8 bit, and no parity with
alternate baud rates of 2400, 4800, 19200, and 38400. The signals present are
RXD, TXD, and ground through the 9-pin D connector on the back panel of the
unit.