Configuring 4-20 mA Output
Chapter 5 4-20 mA Output Option
IsoAir 310P Aerosol Particle Sensor Operations Manual
Page 5-3
Particle Channel Scale Considerations
The maximum counts or concentration that can be monitored is the same as the scale
factor. In other words, if the scale for channel 1 is set to 100, then the output will be
20
mA, when the counts read 100. If the counts are 105, or 2000, the output will still be
20
mA. The particle channels are scaled based on the selection for raw or normalized
counts.
The counts recorded at a given scale are a function of the accuracy and resolution of
the instrument reading the channel, as well as the accuracy and resolution of the
IsoAir 310P particle sensor output. The sensor’s resolution is about 0.025 mA, and the
accuracy is better than 1% of full scale. If the recording device is perfect, and only
sensor errors are seen, then the performance will be as follows:
• If a channel is set to 1000 for the scale, then the readings will be within 10 counts,
i.e., 1%.
• The minimum detectable change is about 2 counts, i.e., 1000/(16 mA/0.025 mA) or
1.56.
In summary, setting the scale factor is a balance between setting the scale large
enough to cover the worst case expected count output, while at the same time setting
it small enough to accurately show normal events.
Software Setup for 4-20 mA Output (Optional)
The IsoAir 310P particle sensor has available serial commands to set the 4-20
mA
outputs. These can be accessed either by the serial setup port on the instrument using
HyperTerminal, or Telnet (if the instrument has been configured for TCP/IP
communications). Before setting the parameters, execute a “status” command to
verify that the 4-20 mA option is detected. If the option is disabled, contact Particle
Measuring Systems for additional information.
