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As a policy of continual improvement, STAUFF reserves the right to alter the specification without prior notice.
201.031
Date of Issue: 06 November 2018
6.4.1.2.1 Null Values
For all formats, the special value -32768 (0x8000 hex) is used to repr
esent a “null” or “no result”
condition. This enables “No Result” to be distinguished from a 0/0/0 ISO code, for example. “No Result”
could be due to an error condition, or to a measurement not having been commanded yet. This
convention is also used for other parameters such as temperature and water content measurements,
where applicable.
NOTE: User written programs should take note, to avoid displays like -32768/-32768/-32768 appearing
on their front panels.
6.4.1.2.2 ISO4406
ISO 4406 defines a set of code values to represent ranges of counts of particles greater than the
nominated sizes of ≥4, ≥6 and ≥14μm(c). The LPM can display codes from 0 to 24. The three-part code
is available in the first 3 RESULT CODES.
We additionally make available equivalent co
des for the other sizes from 21 to 70μm(c), as per Table 6B.
6.4.1.2.3 NAS 1638/ AS4059E-1/ ISO11218
These assign code numbers for the particle counts in each size
range shown in the table. The “basic”
class is then the highest of these individual codes. The basic class is in the first register, with the
individual classes made available in the registers shown.
For these standards there is a complication in that they a
ll define an additional class “00”. This is an
extra “cleaner than class 0” class. We distinguish this from 0 using the numeric value -1. Negative
numbers are represented i
n a Modbus register using the “twos complement” notation. If the user
program interprets this as a positive number it will appear as 65535 (0xFFFF hex).
Classes range from 00(-1) to 12.
6.4.1.2.4 AS4059E-2
AS4059E Table 2 also has some similarities to NAS1638. In terms of the representation in Modbus
registers, the main differences are an extra 4-
6μm(c) size range and the addition of an extra “000” class.
This is represented using the number -2. If the user program interprets this as a positive number it will
appear as 65534 (0xFFFE hex).
6.4.1.2.5 Temperature and Water Content Measurements
These are contained in the TEMPERATURE register 33 and the RH (relative humidity) register 34.
These are scaled by a factor of 100, so that values of 12.34°C and 56.78% RH would be represented by
values of 1234 and 5678 respectively. The temperature can go nega
tive, in which case the usual “twos
complement” representation is used. Most controllers should have a facility for reading “signed integers”
encoded in this way (these will appear as large positive numbers if interpreted instead as positive
numbers, for example 65535).
The special value -32768 (0x8000 hex) is again used to indicat
e ``No result’’, as per the contamination
result codes. This could be due to a sensor failure or to the unit still in the process of powering up.