Model 8712C/U/H Magnetic Flowmeter Transmitters
4-4
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. Both non-scaled D/A trimming and scaled D/A trimming
allow you to trim the 4-20mA output to approximately ±5% of the
nominal 4mA end point and ±3% of the nominal 20mA end point. 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 (select CHANGE on the 275) 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.
Electronics Trim
Electronics trim is the function by which the factory calibrates the
transmitter. This procedure is rarely needed by customers. It is only
necessary if you suspect the Model 8712C/U/H is no longer accurate.
A Rosemount Model 8714 Calibration Standard is required to complete
an electronics trim. Attempting an electronics trim without a Model
8714 may result in an inaccurate transmitter or an error message.
Electronics trim must be performed only with the coil drive mode
set to 6 Hz and with a nominal flowtube calibration number stored in
the memory.
NOTE
Attempting an electronics trim without a Model 8714 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 power down the Model 8712C/U/H to clear the
message. If the trim was completed or no error message appears,
correction requires a Model 8714B or Model 8714C.
To simulate a nominal flowtube with the Model 8714, you must change
the following four parameters in the Model 8712C/U/H:
1. Tube Calibration Number—1000015010000000
2. Units—ft/s
3. Analog Output Range—20 mA = 30.00 ft/s
4. Analog Output Zero—4 mA = 0 ft/s
5. Coil Pulse Mode—6 Hz
The instructions for changing these parameters are located in the
parameter descriptions in this section.
Set the loop to manual, if necessary, before you begin. Complete the
following steps:
1. Power down the transmitter.
2. Connect the transmitter to a Model 8714 flowtube simulator.
3. Power up the transmitter with the Model 8714 connected and
read the flow rate. The electronics need about a 30-minute
warm-up time to stabilize.
HART Fast Keys 1, 2, 4, 2
LOI Key N/A
HART Fast Keys 1, 2, 4, 3
LOI Key Aux. Function
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