Analog 4-20mA Modes
61
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We use an "out of range" current of >20mA (24mA) to indicate parameter not
available
•
The sequence is then repeated.
20.2.1 RH Coding
The RH value is encoded according to the formula
𝑚𝐴 = 6 + (𝑅𝐻 % /10)
(20.1)
or
𝑅𝐻% = (𝑚𝐴 − 6) × 10
(20.2)
So 0% RH = 6mA, 100% RH = 16mA (max legal measurement value), unavailable
= 24mA.
20.2.2 Temperature Coding
The temperature in degrees C is encoded according to the formula
𝑚𝐴 = 10 + (°𝐶/10)
(20.3)
or
°𝐶 = (𝑚𝐴 − 10) × 10
(20.4)
20.2.3 NAS1638, AS4059E1, ISO11218
Parameters are output in the sequence
<SYNC> <CLASS> <CLASS 5-15um> <CLASS 15-25um> <CLASS 25-50> <CLASS
50-100> <CLASS 100+> <RH> <TEMP> <...>
These contamination classs are encoded as
𝑐𝑙𝑎𝑠𝑠 = 𝑚𝐴 − 7
(20.5)
For example: Class 00 = 6mA, Class 0 = 7mA, Class 1 = 8mA, ... Class 12 =
19mA, Off scale = 20mA.
Summary of Contents for ICM
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