Rosemount 8712, Справочное руководство

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Reference Manual
00809-0100-4664, Rev BA
January 2010
Rosemount 8712
4-14
Trims
Trims are used to calibrate the analog loop, calibrate the transmitter, re-zero
the transmitter, and calibrate the transmitter with another manufacturer’s
sensor. Proceed with caution whenever performing a trim function.
D/A Trim
The D/A Trim is used to calibrate the 4-20 mA analog loop output from the
transmitter. For maximum accuracy, the analog output should be trimmed for
your system loop. Use the following steps to complete the Output Trim
function.
1. Set the loop to manual, if necessary.
2. Connect a precision ammeter in the 4–20 mA loop.
3. Initiate the D/A Trim function with the LOI or Handheld
Communicator.
4. Enter the 4 mA meter value when prompted to do so.
5. Enter the 20 mA meter value when prompted to do so.
6. Return the loop to automatic control, if necessary.
The 4–20 mA trim is now complete. You may repeat the 4–20 mA trim to
check the results, or use the analog output test.
Scaled D/A Trim
Scaled D/A trim enables you to calibrate the flowmeter analog output using a
different scale than the standard 4-20 mA 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
allows you to trim the flowmeter using a scale that may be more convenient
based upon your method of measurement.
For example, it may be more convenient for you to make current
measurements by direct voltage readings across the loop resistor. If your loop
resistor is 500 ohms, and you want to calibrate the meter using voltage
measurements made across this resistor, you could rescale your trim points
from 4-20mA to 4-20mA x 500 ohm or 2-10 VDC. Once your scaled trim
points have been entered as 2 and 10, you can calibrate your flowmeter by
entering voltage measurements directly from the voltmeter.
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 you suspect the
Rosemount 8712 is 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. Digital trim must be performed only with the
coil drive mode set to 5 Hz and with a nominal sensor calibration number
stored in the memory.
Field Comm. 1, 2, 5
LOI Key AUX. FUNCTION
Field Comm. 1, 2, 5, 1
LOI Key AUX. FUNCTION
Field Comm. 1, 2, 5, 2
LOI Key AUX. FUNCTION
Field Comm. 1, 2, 5, 3
LOI Key AUX. FUNCTION