Meriam MFT 4010 Modular Calibrator_HART Communicator - Manual (Page 105)

100
3.1 Module Only method makes use of external precision resistors to calibrate the module’s resistance
measurement. The module is set up to allow calibration using precision 10 Ω, 100 Ω, or 1000 Ω
resistors rated for a total tolerance of 10 PPM. The user selects the best resistor value for the types of
RTDs the RIO4000 will be used to calibrate.
One connector (P/N A900442-00026) is needed for each precision resistor used. A10 Ω, 100 Ω, or 1000
Ω precision resistor is connected to pins 3 & 4 and 5 & 6 as though a 4-wire RTD were being connected
(many precision resistor are available in a 4-wire configuration). In addition, an Rs resistor
corresponding to 10, 100, or 1000 Ω should be connected across pins 1 and 2 of the connector. The Rs
resistor allows the MFT to automatically determine which precision calibration resistor is connected. For
10 Ω the Rs value is 14.7 Ω, for 100 Ω the Rs value is 26.1 Ω and for 1000 Ω the Rs value is 825 Ω.
Make sure the external precision resistor is securely engaged in the RIO4000 connector.
Wiring
between the connector and the precision resistor should be of the same size and of the same length.
Field calibrations performed using the
Module Only method should use precision resistors rated for 10
ppm total tolerance at most to replicate the original factory accuracy.
Selecting the Module Only option and connecting a 100 Ω precision resistor causes the following
display to appear.
Cal Res is the actual value of the connected calibration resistor. Edit this value by selecting “Edit Cal
Res Value menu option.
Old Ref is the resistance value from the RIO4000 module memory that was
used in the previous calibration. New Ref is the present resistance measured by the module with the
precision resistor connected. The MFT uses the ratio between New Ref and Cal Res to determine the
new calibration coefficient. Press the Save soft key to store the new calibration point. Repeat the
process by alternately connecting a 1000 Ω precision resistor and a 10 Ω precision resistor to calibrate
the full RIO4000 range.
If the Cal Res value does not need to be edited, the user may move the cursor down to the Calibrate
option on the Module Only Recalibration Screen and press Select. The calibration is completed and
the following display is shown as confirmation.
RTD Calibrate
Standard: 100
Ω Cal R
Edit Cal Res Value
Calibrate
Cal Res = 100.000
Old Ref
= 100.165
New Ref = 100.164
Adjusted = 99.999
Up Down Select Back
Module Only Recalibration Screen
RTD Calibrate
Calibration complete
Date: 2004-05-20
Remove Cal Resistor
OK
Module Only Calibration
Confirmation screen