WMA-5 Operation Manual V. 1.01
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Connecting WMA-5 to External Devices
The WMA-5 has many features and options for communicating with external devices including analog,
digital, and if the WiFi option is installed, wireless.
Analog Voltage Output
One analog voltage output is available for the current CO2 reading. The full scale output is 2.5V and the
CO2 concentration corresponding to full scale can be user set in the Main > Settings > Analog Output
screen. 0 Volts always corresponds to 0 ppm CO2. The analog voltage output is located on the terminal
block at the pins labeled Vout (positive) and GND (negative).
4-20 mA Analog Current Output
One analog current output is available for the CO2 reading. The full scale output is 20 mA and the CO2
concentration corresponding to full scale can be user set in the Main > Settings > Analog Output screen.
4 mA always corresponds to 0 ppm CO2. The user must supply a fixed loop voltage of 12 to 30 VDC to
the terminal labeled Supply 4-20 mA. This supply voltage can come from an external voltage source, or
from the 12V out terminal if an external source is not desired (using a small jumper wire). An external
voltage source should be grounded to the WMA-5 ground at one of the GND terminals. The current
output is then produced between the terminal labeled Iout 4-20mA (positive) and the terminal labeled
GND (negative). A shunt resistor, often 250 Ohm, is normally used at a data logger to convert the current
output into a voltage. With a 12V supply voltage, the 4-20 mA can operate with a combined loop
resistance (shunt resistance plus cable resistance) of approximately 500 Ohm or less. With a 30V supply
voltage, the combined loop resistance can be 1200 Ohm or less.
Alarm Relay Outputs
There are two normally open relay contacts that are activated (closed) when the Low CO2 Alarm (Alarm
1) or High CO2 Alarm (Alarm 2) condition occurs. The Alarm limits are set in Main > Settings > Alarms.
The relays are rated for 30 VDC 1A or 125 VAC 0.3 A. One of the 5V out or 12V out terminals could be
jumpered to one side of these relays to get a 0 to 5V or 12V output signal to trigger an external device
such as a computer, solenoid value or, warning light.
USB Memory Stick
The USB Type A jack on the front panel is designed specifically for a USB Flash Memory Stick. Any
memory stick can be used, however the low profile memory stick provided with the WMA-5 will also allow
the enclosure cover to be closed with the memory stick installed.
It is recommend to format the memory stick to a 512 sector with 32 bit FAT for best performance.
Data collection begins when a Memory Stick is inserted into the USB port on the WMA-5. Data collection
ends when the Memory Stick is removed from the USB port. The data format used is what has been
defined for the Measure Memory Format in the Memory Measure Settings screen. The time interval used
is what has been defined for the Memory Measure Interval in the Memory Measure Settings screen.
When the memory stick is inserted the first time, a directory called “WMA5“ is created. A filename is
created within the directory using the following format:
YYMMDDWI.txt
