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Commissioning
Proline t-mass 65 PROFIBUS DP/PA
84
Hauser
7.9
Adjustment
7.9.1
Zero point adjustment
Calibration takes place under reference operating conditions. (
113).
Consequently, the zero point adjustment is generally
not
necessary!
At zero flow conditions, the output of most thermal mass flow devices has a strong depen-
dency on the process pressure. The effect on the true zero point of the device, by the static
line pressure, is dependant on the gas type and the application demands and in many cases
the use of the low flow cut-off function is adequate to zero the device output.
With some gases and/or a combination of high pressures, zero point adjustment must be
performed under process conditions so that the measuring device can measure smaller val-
ues.
Therefore, the zero point adjustment is advisable in the following special cases:
• To achieve highest measuring accuracy with very small flow rates.
• Under process or operating conditions where the gas properties (heat capacity and ther-
mal conductivity) will change e.g. Hydrogen and Helium.
Preconditions for a zero point adjustment
Note the following before you perform a zero point adjustment:
• A zero point adjustment can be performed only with gases that contain no solid contents
or condensate.
• The adjustment is performed with the process gas at zero flow and at operating pressure.
This can be achieved, for example, with shutoff valves upstream and/or downstream of the
sensor or by using existing valves and gates.
– Normal operation
valves 1 and 2 open
– Zero point adjustment
with
pump pressure
Valve 1 open / valve 2 closed
– Zero point adjustment
without
pump pressure
Valve 1 closed / valve 2 open
A0003601
Fig. 44:
Zero point adjustment and shut-off valves
"
Caution!
You can view the currently valid zero point value using the ZERO POINT function in the SEN-
SOR DATA group (see the "Description of Device Functions" manual, BA000114D/06/…).
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Содержание Proline t-mass 65 PROFIBUS DA
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