Meriam MFT 4010 Modular Calibrator_HART Communicator - Manual (Page 69)

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The MFT will send commands to set the HART device output to 4.000 mA. Select OK to set 4mA output.
Verify the output of 4.000 mA using a reliable external multimeter. If the multimeter measurement does not
confirm the 4mA, enter the trim value at the underscore ( _ ) prompt. Use the Inc & Dec key to manually
adjust the value measured by the external multimeter. A prompt will appear: Save new data? Press the
Yes soft key to accept the changes and implement the 4 mA trim. Pressing No will take you back to the
Analog Trim main menu screen without saving changes.
Then prompt will appear: Fld dev output 4.000mA equal to reference? (Yes/No)
Select ‘yes’ if multimeter shows the 4 mA reading.
If ‘yes’ is selected, then MFT will send command to set 20mA output.
Same procedure is repeated for 20mA trim function.
After 20mA trim completed, the prompt will appear Returning fld dev to original output.
The screen will display the prompt: Loop may be returned for automatic control. This notice reminds the
user to reconnect the device under test to the receiving device. Press the OK soft key to continue and
screen will return to the Analog Trim screen. Pressing Back again will return the MFT to the Config Menu
main screen.
Scaled D/A Trim:
Scaled D/A Trim is a feature that allows HART
® communications users to trim a smart transmitter’s 4-20 mA
output using a different analog scale to measure the loop current. For example, an I/O resistor is commonly
placed in series with the two wire 4-20 mA loop to convert the current signal into a voltage signal for use by
the DCS. By measuring the voltage across the I/O resistor, the loop current value can be obtained by
dividing the voltage by the resistor value. Scaled D/A Trim allows the user to enter this voltage directly
instead of having to convert it into the actual current value. During the trim function, the transmitter output is
set to a fixed output (first 4 mA and then 20 mA). The user is prompted to enter the meter reading using the
analog scale selected by the user. The transmitter D/A calibration trim is then adjusted to obtain the correct
meter reading. The resulting calibrated loop delivers a precision voltage signal to the DCS.
To use Scaled D/A Trim, first make connections to the HART transmitter of interest and press the HART
key. Once communication is established, select the Device Configuration option on the first display, then
Diagnostics, then Calibrate, then Analog Trim and finally Scaled D/A Trim (these menu paths and titles
may vary with HART device). The screen will prompt: “Loop should be removed from automatic control.”
This notice reminds the user that the device output will not be a measurement of the actual process, and to
place the receiving device or control system (such as a chart recorder, PLC, or DCS) in manual mode. Use
the Select soft key to accept OK. Press the Abrt (Abort) soft key to return to the previous screen without
making changes and without taking the device offline.
If OK is selected, the following display will appear:
Scale Options & Corresponding I/O Resistor Values
1.0 to 5.0 volts corresponds to 250 ohm I/O resistor
1.2 to 6.0 volts corresponds to 300 ohm I/O resistor
2.0 to 10.0 volts corresponds to 500 ohm I/O resistor
HART
3144 Temp: DOF TEST
Select Trim Scale:
1.0 to 5.0 volts
1.2 to 6.0 volts
2.0 to 10.0 volts
User Defined
Up Down Select Abrt
Select Scaled D/A Trim Display