FMC Corporation - Talstar 80 - Handbuch (Seite 62)

Commissioning Proline Promass 80 PROFIBUS PA
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6.7 Adjustment
6.7.1 Zero point adjustment
All measuring devices are calibrated with state-of-the-art technology. The zero point obtained in
this way is printed on the nameplate.
Calibration takes place under reference operating conditions.
→ Page 92 ff.
Consequently, the zero point adjustment is generally not necessary!
Experience shows that the zero point adjustment is advisable only in special cases:
• To achieve highest measuring accuracy also with very small flow rates.
• Under extreme process or operating conditions (e.g. very high process temperatures or very high
viscosity fluids).
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 fluids that have no gas or solid contents.
• Zero point adjustment is performed with the measuring tubes completely filled and at zero flow
(v = 0 m/s). 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. 35: Zero point adjustment and shutoff valves
"
Caution!
• If the fluid is very difficult to measure (e.g. containing entrained solids or gas) it may prove
impossible to obtain a stable zero point despite repeated zero point adjustments. In instances of
this nature, please contact your E+H service center.
• You can view the currently valid zero point value using the ZERO POINT function (see the
"Description of Device Functions" manual).
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