Channel Particle Scale Considerations
Lasair II Particle Counter Operations Manual Page J-7
4-20 mA Out Particle Channel
The status channel can be examined either as a single level check, or as bit mapped
error bits. In the simplest test, the output will be 18.25 mA if the box is on, no
alarms are set, and sampling is taking place. If something is wrong, the output will
be 17.5 mA or less.
A more complex decoding is a combination of level sensitive and bitmap. If the
sensor is on, a base level of 7 mA is output. If it is off, the output current will be
less than 7 mA.
The status parameters are bit-encoded with 0.75 mA per bit, and the bits are
assigned as follows:
Manifold Position
The manifold position is output at 4 mA if the AM-II is not being used. If it is used,
then each channel is 0.25 mA. Thus channel 1 is 4.25 mA, and channel 32 is 12
mA.
Notes on Setting Particle Scale Factors
Channel Particle Scale Considerations
The maximum counts 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 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
Lasair II particle counter output. Lasair II particle counter resolution is about 0.025
mA, and the accuracy is better than 1% of full scale. If the recording device is
perfect, and only particle counter errors are seen, then the performance will be as
follows:
Sampling_on bit 1 = 0.75 mA
PumpOK bit 2 = 1.5 mA
LaserOK bit 3 = 3.0 mA
Particle Not Alarmed bit 4 = 6.0 mA
When Lasair II particle counter is on, the base-level
output is 7 mA
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