** Caution: Integral 4 - 20mA converters are internally powered and do not require external power.
DO NOT supply any voltage across these terminals as the 4 - 20mA output will be damaged. It is
also important to assure proper grounding of the external recording device such as a PLC, DCS prior
to connecting the 4 - 20mA.
The OMD-625 uses an Isolated 4 - 20mA analog output.
When connecting the 4 - 20mA output, refer to the circuit board pinout in section 2.3
To verify the signal output of the 4 - 20mA circuit is working properly, connect an ammeter across the
(+) and (-) Pins. With no oxygen sensor connector, it should read approximately 4mA. If a sensor is
installed you can verify the signal matches with the following formula:
Signal Output (mA) = [(Reading / Full Scale Range) x 16] + 4
For example, if we are reading 500 ppm on the 1000 ppm range:
Signal Output (mA) = [(500/1000) x 16] + 4
Signal Output (mA) = 12mA
Some PLC’s prefer a 1 - 5V DC analog output. This can be configured through the MENU to change
the output from 4 - 20mA to 1 - 5V DC. Enter the MENU and select SYSTEM, select OUTPUT TYPE
and it will allow you to select either analog output (4 - 20mA or 1 - 5V DC).
The OMD-625 is equipped with a protocol to adjust the 4mA and 20mA signal output to account for
signal degradation over long copper wires. This might occur in the field if you have 100 feet or more
of cable between your OMD-625 and control panel.
To adjust the analog output, hook an ammeter or PLC up to the 4 - 20mA output. Enter the MENU
screen and go to SYSTEM. From here, enter the OUTPUT CAL and it will prompt you to adjust the
4mA output. Press the UP or DOWN button to adjust, keep pressing the button if you need addition
-
al adjustment. Ignore the number on the display as this is an internal calculation, the ammeter or
PLC system would be the appropriate way to verify, once it is reading 4mA hit ENTER. Once complete
it will prompt you to do the same adjustment for the 20mA.
An important note, the sensor can be installed for this adjustment and does not need to be removed
as is the case with competitive equipment. The electronics isolate out the sensor and allow for a
nearly perfect 4mA and 20mA scale adjustment.
If the user prefers to calibrate the PLC by simulating a current such as 4mA, 8mA, 12mA, 16mA or
20mA, please refer to section 3.6.
3.4
Analog Output 4 - 20mA (1 - 5 V DC Optional)
Operation
OMD-625 Oxygen Analyzer
Designed, Tested and Assembled in California, USA
4045 E. Guasti Rd. #203 Ontario, CA 91761 USA : 1-949-398-2879 : [email protected] : www.sso2.com
3.5
Analog Output Adjustment (4mA and 20mA)
