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. . . . CALIBRATION
Zero and span - true zero procedure
Differential pressure,gauge and level.
- Switch on the power supply.
- With no pressure applied to the transmitters, the value read
on the digital milliammeter should be 4 mA ; if it is not 4 mA turn
the zero screw for at least 1 second. After this operation the
reading should move to 4 mA: if no change occurs repeat the
operation.
- Apply to the H ( high ) connection a pressure equal to the upper
range value (URV) and allow time for the pressure to stabilize.
- Turn the span screw for at least 1 second: after this operation
the reading on digital milliammeter should be 20 mA and the
calibration procedure is complete. If no change occurs either
the calibration procedure was not correctly performed or the
span exceeds the limit; correct and repeat the operation.
Absolute pressure
- Switch on the power supply.
- Connect a vacuum source to the process connection and
draw the maximum possible vacuum obtainable. The value
read on the digital milliammeter should be 4 mA ; if it is not turn
the zero screw for at least 1 second. After this operation the
reading should move to 4 mA : if no change occurs repeat the
operation.
- If the value of the calibration span (URV) is less than the
atmospheric pressure gently open the vent valve so increasing
the pressure to the Upper Range Value. If the calibration span
(URV) is greater than the atmospheric pressure then connect
the pressure connection to a pressure source and generate a
pressure corresponding to the URV. Allow time for the pressure
to stabilize.
- Turn the span screw for at least 1 second: after this operation
the reading on digital milliammeter should be 20 mA and the
calibration procedure is complete. If no change occurs the
calibration procedure was not correctly performed or the span
exceeds the limit; apply the correction and repeat the operation.
Zero suppression procedure
Differential pressure,gauge and level.
Two different methods (a) or (b) can be used :
a) After completion of the zero and span procedure above,
apply to the H ( high ) connection a pressure equal to the
pressure to be suppressed. Allow time for pressure stabilization
and then turn the zero screw for at least 1 second. After this
operation the digital milliammeter reading should be 4mA and
the Upper Range Value automatically moved to a value equal
to the sum of the pressure to be suppressed and the previous
calibrated span.
b) Use the zero and span procedure above but apply pressures
equal to the Lower Range Value (LRV) and then to Upper
Range Value (URV), and turning, for at least 1 second, the zero
and span screws respectively.
Absolute pressure
Use the zero and span procedure as previously described, but
apply to the process connection absolute pressures equal to
the Lower Range Value (LRV) and then to the Upper Range
Value (URV), turning, for at least 1 second, the zero and span
screws respectively.
- 18 -
Zero elevation procedure
Differential pressure and level
Two different methods (a) or (b) can be used :
a) After completion of the zero and span procedure above
apply to the L ( low ) connection a pressure equal to the
pressure to be elevated. Allow time for pressure stabilization
and then turn the zero screw for at least 1 second. After this
operation the digital milliammeter reading should be 4mA and
the Upper Range Value (URV) is automatically moved to a
value equal to the sum of the pressure to be elevated and the
previous calibrated span.
b) Use the zero and span procedure above but apply pressures
equal to the Lower Range Value (LRV) and then equal to the
Upper Range Value (URV) and turning, for at least 1 second,
the zero and span screws respectively. The LRV pressure will
be applied to the L connection whereas the URV will be applied
to the L or to the H connection depending upon the whether the
range is all negative or crosses zero.
Gauge pressure
Apply to the process connection, pressures equal to the LRV
and then equal to the upper range value (URV)
correspondingly turn the zero and span screws respectively.
Note - If during the calibration procedure the
readings on the digital milliammeter are outside its
inherent accuracy, output trimming of the transmitter
may be requested. This operation can only be performed
using the Hand Held Terminal Communicator or the
Personal Computer Configurator. If this equipment is
not available the transmitter should be returned to a
Service Center for recalibration.
In some cases, expecially for tank level measurement, the
calibration can also be obtained automatically by the indication
of the actual output percentage, without any calculation for
LRV and URV. The operation is called Output % Reranging
and can be performed using a HART configuration tool (see
Output % Reranging in the ADDENDUM FOR FLANGE-
MOUNTED TRANSMITTER).
WARNING. In order to ensure the correct operation
of the transmitter, after the calibration procedure the
device must be put in operating condition as described in
Table 1, in the section Commissioning and Configuration
Issues.
and
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