Alpha Moisture Systems DS1200-AMT Instrukcja instalacji, uruchomienia i obsługi - Strona 11
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8 Normal Operation
8.1
Analogue 4-20mA Mode (2-wire)
•
In normal operation, the transmitter will produce a 4-20mA signal, which is proportional to the level
of moisture in the gas being monitored. The moisture reading is sampled and up dated once per
second. The AMT has 3020 distinct steps over the 4 to 20mA range corresponding to a resolution of
0.005mA.
9 AMT AutoCal
Warning Do Not power down during the AutoCal process as
this can lead to corruption of the AMTs memory.
•
AutoCal allows the user to ensure accuracy to the laboratory calibration by checking the span of the
transmitter and correcting for any deviation. It should be operated periodically, every 2 to 3 months,
or when verification of the AMT Transmitter is required.
•
The AMT is supplied with an electronic autocal, which allows the calibration span of the transmitter
to be adjusted. The autocal is controlled by the 2 buttons located on the side of the AMT transmitter
labelled 'W' (wet) and 'D' (dry).
Note : - The AMT must be connected to an indicator or some device able to supply an accurate
measurement of the mA output.
9.1
A Pre-conditioning the transmitter
•
To perform the autocal, the transmitter needs to be removed from the process gas at which point the
display/indicator will read the ambient dewpoint or full scale (if the ambient dewpoint level is above
the range of the AMT). Expose the transmitter to the known autocal moisture level and allow the
transmitter to attain equilibrium. (For technical questions and advice on the time taken to attain
equilibrium Contact your AMT supplier)
Method 1: - Expose to a known moisture level. (Applicable to all versions of AMT
Transmitters)
If a known gas is available within the range of the transmitter, then the AMT can be AutoCaled
against this value.
Method 2: - Saturating method. (Only applicable to 0ºC (32ºF) and –20ºC (-4ºF) top end
range AMT transmitters)
When the AMT sensing element is exposed to a dewpoint level above the top end range of the
transmitter, the sensor will saturate and the transmitter can be AutoCaled to 0°C or –20ºC. For both
0ºC and –20ºC AMTs, ambient dewpoint is usually adequate to saturate the sensor.
Method 3: - Set against Ambient moisture level. (Only applicable to 20ºC (68ºF) top end range
AMT transmitters)
When the ambient dewpoint is known, then the AMT can be AutoCaled to the ambient value.
ACAL adjusts slope of curve.
Sensor Reading
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