Solartron Mobrey 7828, Техническое руководство

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Calibration check 7828 Density Transmitter Technical Manual
5-4
78285000_AA
5.3 USER CALIBRATION CHECKS
5.3.1 AMBIENT AIR CALIBRATION CHECK
An air check is a simple and convenient method to see if any long term drift or corrosion
and deposition on the tines has occurred.
Ambient air check procedure:
1. Isolate and, if necessary, disconnect the transducer from the pipeline.
2. Clean and dry the wetted parts of the transducer and leave them open to the ambient
air.
3. Apply power to the instrument and check that the time period of the instrument agrees
with the figure shown on the calibration certificate to within ±100ns. If the 7828 is not
at 20°C, compensate for this by adding an offset of +110ns for every °C above 20°C,
or by subtracting an offset of +110ns/°C below 20°C.
4. Refit the transducer to the pipeline if serviceable or remove for further servicing.
5.3.2 ON-LINE CALIBRATION ADJUSTMENT
An on-line calibration adjustment may be required if:-
a) The physical boundary surrounding the tines is different from the physical boundary
used for the factory calibration.
b) The viscosity of the fluid is greater than 500cP.
c) If the velocity of sound of the fluid is significantly different from the fluid used for the
factory calibration. In practice this affects the density measurement by less than
±1 kg/m
3
.
d) If the unit has suffered long term drift or corrosion of the tines.
The 7828 is a very accurate and stable instrument, and will normally provide good
measurements. If it is suspected of giving incorrect results, you should confirm this by
carefully checking the integrity of the fluid temperature measurement, and compare this
with the temperature measurement given by 7828. You should also verify the integrity of
the density check measurement. It is only after you have eliminated all other possible
causes of error that you should attempt to make adjustments to the calibration of 7828.
Normally the calibration adjustment is made by configuring a simple density offset into the
instrument. If a more detailed calibration adjustment is required, such as a 2 or 3 fluid
calibration adjustment for offset and scale, then refer to Solartron.
Calibration adjustment - stable liquids:
1. Using ADView (see chapter 4), reset the line density offset (register 173) to 0, and the
line density scaling factor (register 174) to 1.
2. Ensure that the system has reached its stable operating temperature.
3. With the 7828 operating at typical process conditions, draw off a sample of the liquid
into a suitable container, and note the 7828 density reading and the operating
temperature.