6 Commissioning PROline Promass 80
52 Endress+Hauser
6.2.3 Zero point adjustment
All Promass 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 (see Page 84). Consequently, the zero point adjustment
is generally not necessary for Promass.
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 contain no gas or solid
contents.
• A 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 shut-off valves
upstream and/or downstream of the sensor or by using existing valves and gates
(Fig. 24):
– 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
"
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).
Fig. 24: Zero point adjustment and shut-off valves
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