Multiple Trim Operation - ABB 691HT Operating Instructions Manual

R e t u r n i n g X m t r to
o r i g i n a l o u t p u t
4-20 m A T R I M - CHOOSE
INTERNAL SCALE
OTHR 4 TO FACT
SCALE 20mA T R I M
T r i m w i l l b e s e t
a s a t f a c t o r y

Multiple Trim Operation

If the previous operation aborts because the passed
parameter is too large or too small then multiple trim is
necessary.
The 4 mA trimming should be done first. If the output
looks saturated, i.e. the reading is around 3.75 mA (or
0.938 Volt if 1 to 5 Volt scale has been selected ) enter
the value 3.25 mA (or 0.81 Volt) until the output
desaturates and then the value read on the reference
meter. If the reading is above 4.8 mA enter the value
4.75 mA until the reading falls below 4.8 and then the
value read on meter.
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When the procedure has been completed the screen shows for some
seconds the display aside. This notice will be followed by the message:
"WARNING - Loop may be returned to auto" Press PROCEED to
acknowledge .
As already mentioned, a third option is available for 600T and 600T EN
pressure transmitter and for 652/653 S Temperature transmitter to allow
the user to restore the original factory calibration. Selecting with the F3
key this option the following warning message will be displayed:
"WARNING - Control loop should be in manual - PROCEED". Pressing
the PROCEED key to acknowledge the message and continue the
following display appears: the user can abort the procedure pressing
ESCape or accept the selection pressing F4 to PROCEED . In this case
the small T blinks in the upper right corner signalling that the appropriate
P R O
command is sent to the transmitter. A warning message warns that the
C E E D
control loop, if necessary, can be returned to automatic control. Press F4
to return to the 4 to 20 mA Trim menu.
Proceed in the same way for the 20 mA trimming. If the
output looks saturated, i.e. the reading is 21 mA enter
the value 20.8 until the output desaturates and the
reading falls below 21 mA, then introduce the meter
reading.
If the reading is less than 19.2 mA enter the value 19.3
mA until the reading rises above 19.2 and then introduce
the reference meter reading. If the value does not rise
to 20 mA check the transmitter power supply.