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3.5 Input Isolation Option “-I”
The 1250-LTC may be ordered with isolated synchro input terminals. In cases where
there is a compromise of the (Controller, SCADA, etc…) analog input’s isolation to earth
ground, this Isolation Option will prevent AC voltage from becoming impressed upon the
1250-LTC’s analog output signal to that device. (See Note at the end of Section 3.1, page 39)
This option consists of two signal isolation transformers installed in the signal input circuitry.
Performance and reliability are not affected when this option is installed.
Please note that this option is not compatible with the Relay Option (-R). The “-I” and
“-R” options can not be installed simultaneously. They occupy the same space inside the
instrument. You must choose one or the other.
4.0 FIELD CALIBRATION & TEST
Calibration: The Model 1250-LTC should not require field calibration. However,
there are provisions in the menu to facilitate Signal Input Calibration and Analog Output
Calibration. Signal Input Calibration cannot be performed in the field; it is strictly an in-
factory function. The analog output may be adjusted in the field. A calibrated multi-meter
should be used to measure the output signal during calibration.
To enable analog calibration, select the OP 30, CAL menu command and choose the
“On” mode. If you are using the RS-232 serial port, use the ANACAL command. The
analog output may be forced to LOW, MID, and HIGH output signal states.
If menu commands are being used, select the OP 31, L CAL command to force the
analog output to LOW scale output. If you are using the RS-232 serial port, press the space
bar on the computer terminal. This toggles the output between LOW, MID, and HIGH
outputs. The display on the 1250-LTC should read “LO”. The analog output low scale may
now be adjusted by turning the “ZERO” pot, accessible through the slot in the left side of the
case (see Figure 4.1), until the output signal is reading properly on the multi-meter.
If menu commands are being used, select the OP 32, H CAL command to force the
analog output to HIGH scale output. If you are using the RS-232 serial port, press the space
bar on the computer terminal. The display on the 1250-LTC should read “HI”. The analog
output high scale may now be adjusted by turning the “SPAN” pot (see Figure 4.1) until the
output signal is reading properly on the multi-meter. Repeat analog LOW and HIGH
calibration steps several times to assure proper output signal calibration of both. Some
interaction may occur between the ZERO and SPAN adjustments.
If menu commands are being used, select the OP 33, D CAL command to force the
analog output to MID scale output. If you are using the RS-232 serial port, press the space
bar on the computer terminal. The display on the 1250-LTC should read “--”. The analog
output should read a mid-scale signal on the multi-meter. There is no adjustment for this mid-
scale output.
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