S&C Instruction Sheet 768-550 27
Calibration
Calibrating the Voltage- and Current-Sensor
Outputs
Switch-control units using external ac control power can
accommodate 5 Vac or 69 Vac voltage-sensing outputs.
Switch-control units using self-contained ac con trol power
can accommodate only a 5 Vac voltage sensing output.
Locate the yellow card included in the “Installation and
Operation Information Kit” shipped with the switch. This
card contains the precise magnitude ratios and phase-angle
shifts of each current sensor and voltage sensor included on
the switch.
For RTUs having 5-Vac voltage-sensing inputs:
Sensor data written on this card can be used directly to
calibrate the voltage-sensing and current-sensing inputs
to the RTU. Refer to the manufacturer’s literature for
cal ibration instructions.
For RTUs having 69-Vac voltage-sensing inputs:
Voltage sensor magnitude ratio(s) written on this card do not
apply. Each voltage sensor magnitude ratio must be adjusted
to take into account the sensor’s nominal 69-Vac output in
these applications and the adjusted magnitude ratio used to
calibrate the corresponding voltage-sensing input to the RTU.
To determine the adjusted voltage-sensor magnitude
ratio(s), measure and record the voltage-sensor output
voltage(s) on the terminal strip of the switch control or
burden board. The procedure is as follows:
STEP 1.
Attach voltmeter probes to the terminals connected
to the voltage sensors. Refer to Table 3 on page 31
for switch control and output termi nals.
STEP 2.
Place the voltage-sensor output selector switch on
the switch control or burden assembly in the
5 Vac
position. Measure and record the voltage, V1.
STEP 3.
Place the voltage-sensor output selector switch on
the switch control or burden assembly in the
69 Vac
position. Measure and record the voltage, V2.
STEP 4.
Calculate and record the following:
Adjusted voltage-sensor magnitude ratio =
×
(voltage-sensor magnitude ratio
where voltage-sensor magnitude ratio is the value
written on the yellow card.
▲
STEP 5.
Repeat Steps 1 through 4 for each voltage sensor
pro vided.
For Type CCU-SP (catalog number 54215), the output
terminals are located on the S&C Switch Control.
For Type CCU-XP (catalog number 54216), the output
terminals are located on the bottom half of the S&C Voltage
Sensor Burden Assembly.
