Yokogawa digitalYEWFLO (DY) - Manual (Page 68)

MAINTENANCE
IM 1F2B4-01-YIA
Page 72
4.1.14 Trimming the 4-20 mA analog output
The 4-20 mA analog output circuit is accurately calibrated at the factory using precision test equipment.
Field adjustment of this circuit is rarely required. This adjustment should not be made when there is a
suspected offset of the 4 mA point due to noise such as pipe line vibration, in this case, please refer to
signal conditioning.
If you find it necessary to trim the 4 mA and/or 20 mA value, it can be adjusted digitally with the
handheld terminal. An example of when to use this adjustment would be when there is a 250
Ω
resistor in
the loop changing the output to 1 - 5 volts. If the resistor value is not exact, an offset error of either the 4
mA (1V) and/or 20 mA (5V) reading will occur.
To digitally trim the current output, refer to the following formula and example to determine the correct
digital trim parameter settings. The parameter H08 :Trim 4mA is used to adjust the 4 mA (or 0%) output,
and parameter H09 :Trim 20mA is used to adjust the 20 mA (or 100%)
H :Maintenance BT200 handheld terminal BT100 handheld terminal
H08 :TRIM 4ma
0.45 % Move to parameter H08, re-enter the
value shown, (.45 this example) press
Enter twice. The output will go to
0%. (Don’t press OK until you are ready
to leave this parameter). Move to parameter H08 and press e
nt
twice.
Read the analog output at 0% and record it as X (3.93mA this example).
Record the original value of H08 (0.45 this example).
H09 :Trim 20ma
1.25 % Move to parameter H09 and re-enter the
value shown, (1.25 this example) press
enter twice. The output will go to
100%. (Don’t press OK until you are
ready to leave this parameter). Move to parameter H09 :TRIM 20ma and
press e
nt twice.
Read the analog output at 100% and record it as Y (19.72mA this example).
Record the original value of H09 (1.25 this example).
Calculate the New H08 setting using X and Y from above in Equation 1.
Calculate the New H09 setting using X and Y from above in Equation 2.
H08 :TRIM 4ma
0.8993 % Store the New H08 setting (confirm the output goes to 4 mA or 0%).
H09 :Trim 20ma
2.58% Store the New H09 setting (confirm the output goes to 20 mA or 100%).