153
Reference Manual
00809-0300-4750, Rev CA
March 2016
8.6.2
Scaled D/A trim
A
scaled D/A trim
enables calibration of the flowmeter analog output using a different scale
than the standard 4-20mA output scale. Non-scaled D/A trimming (described above), is
typically performed using an ammeter where calibration values are entered in units of
milliamperes. Scaled D/A trimming enables trimming of the flowmeter using a scale that
may be more convenient based upon the method of measurement.
For example, it may be more convenient to make current measurements by direct voltage
readings across the loop resistor. If the loop resistor is 500 ohms, and calibration of the
meter will be done using voltage measurements across this resistor, the trim points can be
rescaled from 4-20mA to 4-20mA x 500 ohm or 2-10VDC. Once the scaled trim points have
been entered as 2 and 10, calibration of the flowmeter can be done by entering voltage
measurements directly from the voltmeter.
8.6.3
Digital trim
Digital trim
is the function by which the factory calibrates the transmitter. This procedure is
rarely needed by users. It is only necessary if the Rosemount 8750W is suspected to be no
longer accurate. A Rosemount 8714D Calibration Standard is required to complete a
digital
trim
. Attempting a
digital trim
without a Rosemount 8714D Calibration Standard may result
in an inaccurate transmitter or an error message. The
digital trim
must be performed with
the coil drive mode set to 5Hz and with a nominal sensor calibration number stored in the
memory.
Note
Attempting a
digital trim
without a Rosemount 8714D Calibration Standard may result in an
inaccurate transmitter, or a “DIGITAL TRIM FAILURE” message may appear. If this message
occurs, no values were changed in the transmitter. Simply cycle power on the Rosemount
8750W to clear the message.
LOI menu path
Field Mount: Device Setup, Diagnostics, Trims, Scaled D/A Trim
Wall Mount: N/A
Traditional Fast Keys
1, 2, 5, 2 or 1, 4, 2, 1, 7
Device dashboard
3, 4, 4, 6
LOI menu path
Field Mount: Device Setup, Diagnostics, Trims, Digital Trim
Wall Mount: AUX. FUNCTION
Traditional Fast Keys
1, 2, 5, 3
Device dashboard
3, 4, 5
Содержание Rosemount 8750W
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