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Control. Monitor. Protect
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T
7900
Electronic Potentiometer
• Electronic Potentiometer with voltage, current or
PWM output
• Wide selection of output ranges
• Isolated outputs
• Adjustable ramping times
• 2 LEDs indicating “increase” and “decrease”
• Preset push button defines the output reference
• Programmable power reference unit for operation of
generators in parallel with the grid
• 50 hour burn-in before test
• Flame retardant enclosure
Application
The T7900 Electronic Potentiometer is
typically used as an interface between in-
crease and decrease contacts and a device
requiring control / adjustment by a voltage
or current signal, such as an electronic
speed controller.
In such applications, the T7900 acts in
a very similar manner to a motorized
potentiometer, except that the outputs are
a voltage, a current or a pulse width mod-
ulated signal (PWM), while the motorized
potentiometer has a variable resistor
output.
In generator control applications, the
T7900 can be used together with e.g. the
SELCO T4500 Auto Synchronizer and the
T4800 Load Sharer.
The T7900 converts the increase and
decrease pulses (from e.g. the T4500 and
T4800) into a suitable analog voltage or
current signal. This analog output sig-
nal can be used as a control input to an
electronic speed controller.
The analogue outputs from T7900 are
isolated. The rise and fall time of the
output signal can be individually adjusted
to match the response time of a specific
speed governor or voltage regulator. The
slope of the output signal is not limited by
mechanical aspects, unlike a conventional
motorized potentiometer, which is limited
by the RPM of the internal motor.
A wide number of output ranges can be
selected via dipswitches in order to match
almost any type of speed controller. Addi-
tional ranges can be defined via the option
-
al advanced PC configuration of the T7900,
using a standard ANSI terminal such as the
Windows HyperTerminal.
The unit can also be used as a
programmable power reference unit
for setting the capacity to be provided by
engine driven generators, when the gener-
ators are operated in parallel with the grid
(utility) or a shaft generator. This function
is described on the following pages.
Terminals 1, 2 & 3:
Optional AC supply for the AC versions of T7900
(an alternative to the 24V DC / AC supply).
Terminal 4:
+ 10V output
Terminal 5:
+ Reference of voltage signal for PWM output
Terminal 6:
Output voltage of 0 – 10V DC for connection of a
meter instrument.
Terminals 7, 14 & 19:
Common reference for inputs and outputs.
Terminals 8, 9 & 10:
Output control signals as voltage, current or PWM.
Terminal 11 & 12:
24V DC supply.
Terminal 13:
RESET for reset of output signal back to the reference level.
Terminals 15, 16 &17:
IN1, IN2 & IN3 are control inputs for setting various output
levels when the T7900 is used as a power reference unit.
Terminals 18, 19 & 20:
INCR, REF & DECR are control inputs for the T7900
with increase and decrease pulses.
REF
0-10V
SUPPLY POWER REF.
IN
PWM
±10V 0-20mA
L
1
L
2
24V DC/AC RESET REF IN1 IN2 IN3 INCR REF DECR
Optional
AC supply
+
-
Fig. 1. Connections.
