Yokogawa EJA438 - Manual (Page 27)

IM 1C22J1-01E 6-2
6. OPERATION
6.2 Zero Point Adjustment
Adjust the zero point after operating preparation is
completed.
IMPORTANT
Do not turn off the power to the transmitter
immediately after a zero adjustment. Powering
off within 30 seconds after a zero adjustment will
return the adjustment back to the previous
settings.
The zero point adjustment can be made in either way:
using the zero-adjustment screw of the transmitter or
the BT200 operation.
For output signal checking, display the parameter A10:
OUTPUT (%) in the BT200.
Output signal (%)
display PARAM
A10:OUTPUT(%)
0.0 %
A11:ENGR OUTPUT
A20:AMP TEMP
DATA DIAG PRNT ESC
F0604.EPS
Zero-adjustment
screw
᭹ BT200
᭹ Zero-adjustment Screw
After reviewing this parameter you are prepared to
adjust the zero point. When making the zero adjust-
ment on a pressure transmitter, the process pressure
value does not have to be set to the low limit of the
measurement range (0%). In such case, adjust the
transmitter output signal to the actual measured value
obtained from a high-accuracy pressure measuring
instrument.
6.2.1 When you can obtain Low Range
Value from actual measured value
of 0% (0 kPa, atmospheric pres-
sure);
For pressure measurement using gauge pressure
transmitters, follow the step below before zero point
adjustment.
1) Close the tap valve (main valve).
2) Loosen the fill plug so that the pressure applied to
the transmitter is only the head of the seal liquid.
3) Adjust the zero point at this status.
4) After the adjustment, close the fill plug and then
gradually open the tap valve.
᭿
Using the Transmitter Zero-adjustment
Screw
Before adjusting a screw, check that the parameter
J20: EXT ZERO ADJ displays ENABLE. See
Subsection 7.3.3 (11) for the setting procedure.
Use a slotted screwdriver to turn the zero-adjustment
screw. Turn the screw clockwise to increase the output
or counterclockwise to decrease the output. The zero
point adjustment can be made with a resolution of
0.01% of the setting range. Since the degree of zero
adjustments varies with the screw turning speed, turn
the screw slowly for fine adjustment and quickly for
coarse adjustment.
᭿
Using the BT200
Zero point can be adjusted by simple key operation of
the BT200.
Select parameter J10: ZERO ADJ, and press the
ENTER key twice. The zero point will be adjusted
automatically to the output signal 0% (4 mA DC).
Confirm that the setting value displayed for the
parameter is ‘
0.0% ’ before pressing the ENTER key.
See Subsection 7.3.3 (11) for BT200 operating proce-
dures.
A display when parameter
J10 is selected.
Press key
twice for 0% output 4 mA DC.
SET
J10:ZERO ADJ
–0.0 %
+ 000.0
CLR ESC
F0605.EPS