RFC-1 Installation page 3.9
In some cases it is necessary to use an externally generated voltage to indicate status. Suppose, for example, that a
large AC contactor that does not have auxiliary contacts is to be metered. A small step-down transformer can be
placed across the coil of the contactor to generate a low voltage AC sample. The low voltage AC can then be routed
through a series diode and resistor (approximately 1 KΩ) to the telemetry input. The 10 µF capacitor on the RP-8
should provide sufficient filtering. Do not apply more than 16 volts DC to the telemetry input terminals!
3.3.3 Calibrating Telemetry Readings
Calibrating the telemetry inputs requires basic operational skills with the RFC-1 in local mode. Skip ahead and read
the section that covers operation from the local phone if you have no previous experience with the RFC-1.
Calibrating the telemetry inputs involves adjusting the channel readings so that they correspond to the readings given
from front panel meters. The process is to adjust the calibration pot just behind the front panel for a given channel
while checking the value with the local phone. Tweak the calibration pot until the RFC-1 reads the same reading that
is shown on the corresponding front channel meter. Channels read right to left as viewed from the front of the
panel—the lowest channel number is on the far right. Make sure that you adjust the correct pot for the channel that
you are calibrating.
Figure 3.10; Telemetry calibration point
The calibration pots are 22-turn trimmer resistors that allow precise adjustment. The pots have a clutch at each
extreme to protect the internal mechanism from traveling too far but the pot will turn indefinitely. It does make a faint
clicking sound at each end of travel.
As you adjust the pot, the RFC-1 will read new values automatically if the change is very large. However, as you
close in on the proper value, you will need to reselect the channel to get an updated reading. Take advantage of as
much of the scale as possible. If the normal reading is 100, calibrate the channel to 1000. This is still well within the
upper limit of 2040 and offers much higher resolution than if the channel was calibrated to 0100.
From the factory, the RFC-1 will read a four-digit value between 0003 and 2039 with no decimal point. Programming
options include different scales, a decimal point, unit words and lead zero suppression. The Advanced Operation
section of this manual contains more information.
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