Sel T7900 User manual

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T7900 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 denes 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 specic
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 dened via the option-
al advanced PC conguration 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.

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Electronic Potentiometer Function
When the CONFIG dipswitch no. 1 on the
front is OFF, the T7900 will act as an
electronic potentiometer. The output is a
variable voltage, current or pulse width
modulated signal (PWM).
The type and range of output can be
selected via dipswitches on the back of
the unit. This selection should be made in
order to match the input type and range
of the unit to control e.g. an electronic
speed controller. The following can be
selected on the dipswitches:
Setting all dipswitches to ON will put
the unit in programming mode. In
programming mode the unit can be
congured from a PC using a standard
ANSI terminal such as the Windows Hy-
perTerminal. In this case additional out-
put ranges, reference levels and
other parameters can be specied from
the PC. An optional programming kit
G0100 is available for this purpose.
The control inputs are the increase / de-
crease contact inputs on terminals 18
and
20. As long as no increase / decrease
in-
puts have been received, the output sig-
nal will stay at the reference level.
Fig. 2 illustrates the normal output
characteristic. When an increase signal is
applied to the T7900, the output signal
will increase until the increase signal is
interrupted. The ramping of the increase
is determined by the setting of tINCR in
such a way that lower settings will cause
faster ramps.
When a decrease signal is applied to the
T7900, the output signal will decrease
until the decrease signal is interrupted.
The ramping of the decrease is
determined by the setting of tDECR.
When using a PC for conguration, it is
also possible to select a different type of
output characteristic, a so called “rubber
band” output characteristic where the
output automatically goes back to the
reference level when the increase or
decrease signal is interrupted.
In this case, the ramping of the increase
and decrease is a little different. They are
both the same, determined by the setting
of tINCR, whe reas the ramping of going
back to the reference level is now
determined by the setting of tDECR. This
is illustrated in gure 3.
The ramping times tINCR and tDECR can be
set on the two dials on the front panel.
The ramping times have the following
ranges:
0.25 s / V – 2.5 s / V
0.25 s / mA – 2.5 s / mA
0.04 s / % – 0.4s / %
The ramping time tINCR can be multiplied
by 10 by setting the CONFIG dipswitch
3 to on and the ramping time tDECR can be
multiplied by 10 by setting the CONFIG
dipswitch 4 to ON.
2.5 s / V – 25 s / V
2.5 s / mA – 25 s / mA
0.4 s / % – 4s / %
The function of the CONFIG dipswitches
on the front is as follows:
SW1 ON: POWER REF
SW2 ON: INVERT
SW3 ON: INCR ramp*10
SW4 ON DECR ramp*10
Dipswitch no. 1 should be OFF when
T7900 is used as an electronic
potentiometer, and on when T7900 is
used as a power reference unit.
Dipswitch no. 2 can be used for inverting
the output, e. g. going from 10V to 0V
rather than from 0V to 10V. Dipswitches
nos. 3 and 4 are the dipswitches mentio-
ned previously for multiplying the ramp
times by 10.
The output reference level can be set or
changed by adjusting the output signal to
the desired level and then briey activate
the PRESET push button on the front of
the unit.
PWM Output (terminals 10 and REF)
This type of signal is used as input in
some speed controllers (e.g. Woodward
& Caterpillar) because the signal is found
Output signal
(e.g.voltage)
t
INCR
t
DECR
Input pulse signals
INCR
REF
DECR
SW1 SW2 SW3 SW4 Output Ref.
1 2 4 8
OFF OFF OFF OFF -10V – +10V 0V
OFF OFF OFF ON 0V – +10V +5V
OFF OFF ON OFF -5V – +5V 0V
OFF OFF ON ON -10V – 0V -5V
OFF ON OFF OFF -1V – 0V 0V
OFF ON OFF ON 0V – +1V 0V
OFF ON ON OFF 0V – +3V 0V
OFF ON ON ON 0V – +5V 0V
ON OFF OFF OFF 0V – +6V 0V
ON OFF OFF ON -1V – +1V 0V
ON OFF ON OFF -3V -- +3V 0V
ON OFF ON ON
ON ON OFF OFF 10-90% 2.94KHz 50%
ON ON OFF ON 4mA – 20mA 12mA
ON ON ON OFF 10-90% 500Hz 50%PWM
ON ON ON ON PRG. MODE
Fig. 2. Normal output characteristic.
Output signal
(e.g. voltage)
t
DECR
t
INCR
t
DECR
Input pulse signals
t
INCR
INCR
REF
DECR
Fig. 3. “Rubber band” output characteristic.
50 %
90 %
Fig. 5. Pulse width modulated signal (PWM).
The range of the pulse width is 10% - 90%
in default conguration. The reference
point is 50%. Voltage, pulse and REF can
be altered via PC conguration.
Figure 5 illustrates a PWM signal of 50%
and 90%. The default reference is 50%.
However, this can be changed using PC
conguration or by using the PRESET
push button.
REF 10 54
+10V
REF
1kΩ/
2W
Fig. 4. T7900 PWM Output
less sensitive to noise rather than a volta-
ge or current input.
The PWM output of T7900 is an open col-
lector output with a 1kΩ pull up resistor
as shown in gure 4. In factory default
this output gives +10V when the transis-
tor is closed and 0V (REF) when open. Ex-
ternal voltages can be used by removing
the bridge between terminals 4 and 5 and
connecting and external voltage (max. 24
V DC) between terminals 5 and REF.
The frequency of the PWM signal is
500HZ or 2,94 KHz dependending on the
dip switch settings.

Control. Monitor. Protect
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Figure 6 shows how to synchronize and
share the load using the SELCO T4500
Auto Synchronizer and the SELCO T4800
Load Sharer via the T7900.
Via the T7900 the INCR and DECR
pulses will give a suitable voltage,
current or PWM output signal which will
control the electronic governor. Due to
the wide range of setting possibilities
almost any type of electronic governors
can be controlled.
Power Reference Unit
Funcon
When the CONFIG dipswitch no. 1 on the
front is ON, the T7900 will act as a power
reference unit for setting the capacity to
be provided by engine driven generators,
when the generators are operated in
parallel with the grid (utility) or a shaft
generator.
For such applications, the T7900 can be
used with SELCO Load Sharers T4300,
T4400 or T4800. The output voltage of
T7900 (terminals 8 and 7) is connected to
the parallel lines of the load sharers
(terminals 13 and 12). The load sharer
will now adjust the power of the genera-
tor according to the level of this voltage.
ELEC.
GOV.
ELEC.
POT
T7900
18 19 20
8
7
+
_
+
_
0
11
12
BUS
24V
DC
ELEC.
GOV.
ELEC.
POT
T7900
18 19 20
8
7
+
_
+
_
0
11
12
24V
DC
Figure 6. Application Diagram. Synchronization and load sharing with T4500, T4800 and T7900 using electronic governors.
The output voltage can be set to different
levels using three contact inputs IN1, IN2
and IN3 (terminals 15, 16 and 17) of the
T7900 as described later.
Fig. 6. Application Diagram. T7900 used as a power reference unit with
T4800.
FREQ. OUT. 8
FREQ. OUT. 8
8 V
7 REF
11
12
14 15 16 17
IN1IN2 IN3
24V
DC
MAINS-SWITCH
T7900
MOTOR
SUPPLY
DECR.INCR.
GEN.
1
LOAD SHARER
T4800
LOAD SHARER
T4800
MOTOR
SUPPLY
DECR.INCR.
GEN.
1
BUS
GRID
The same T7900 can be
connected to several load
sharers where a multi engine
installation is operating in
parallel with a grid supply.
The voltage on the parallel
lines of the T4800 Load
Sharer is 0 – 1V DC, where
0V DC corresponds to no
load and 1V DC corresponds
to full load. Therefore, when
the T7900 is used as a power
reference unit with T4800
Load Sharers, the output ran-
ge 0 – 1V DC should be selec-
ted on the dipswitches on the
rear panel of the T7900:
SW1: OFF
SW2: ON
SW3: OFF
SW4: ON
The voltage on the parallel lines of the
T4300 and T4400 Load Sharers is 0 – 3V
DC. Therefore, when the T7900 is used
as a power reference unit with these
load sharers, the output range 0 – 3V DC

»
SELCO
Betonvej 11
DK- 4000 Roskilde
Denmark
Tel.: + 45 - 70 26 11 22
Fax: + 45 - 70 26 25 22
e-mail: [email protected] selco.com
Specications
T7900 Electronic Potentiometer
The T7900 has been approved by major
marine classication societies.
For more information about the indivi-
dual certicates, please visit selco.com
Approvals &
Certicates Fig. 4 Dimensions
The three contact inputs IN1, IN2 and
IN3 of the T7900 will by default set the
following levels of the output voltage
when the contacts are closed (connected
to REF):
IN1: 10% of full level
IN2: 20% of full level
IN3: 40% of full level
This gives the following output possi-bi-
lities:
IN3 IN2 IN1 Voltage
OFF OFF OFF 0%
OFF OFF ON 10%
OFF ON OFF 20%
OFF ON ON 30%
ON OFF OFF 40%
ON OFF ON 50%
ON ON OFF 60%
ON ON ON 70%
When using PC based conguration, the
output levels corresponding to the three
contact inputs IN1, IN2 and IN3 can be
changed to any percentage between 0
and 100%. Please note that the level can
never exceed 100%.
70
115
50
85
7.5
10
100
Fixing holes
2 x ø 4.5 mm
Dimensions in mm
Supply: 8 – 36V DC / AC
Consumption: Max. 120mA at 24V DC
Output ranges: -10V – +10V (or any part of this, e.g. 0V – +1V)
0 – 20mA (or any part this, e.g. 4mA – 20mA)
0% – 100% PWM 500Hz (or any part of this e.g. 10% - 90%)
0% – 100% PWM 2.94MHz(or any part of this e.g. 10% - 90%)
PWM output signal: Frequency: 500Hz of 2,94KHz. Level: 0 – 10V. Default reference: 50%
Increase / decrease 0.25 s / V – 2.5 s / V or 2.5 s / V – 25 s / V
ramp times: 0.25 s / mA – 2.5 s / mA or 2.5 s / mA – 25 s / A
0.04 s / % – 0.4s / % or 0.4 s / % – 4s / %
Resolution: 12 bits or 15 bits
Serial link: RJ11-modular
RS 232 parameters: 9600 bits per second
No parity
8 data bits
1 stop bit
Operating temperature: -20°C to +70°C
EMC: EN50263
Burn-in: 50 hours before final test
Enclosure material: Polycarbonate. Flame retardant
Weight: 0.3kg for T7900-00, 0.5kg for other types
Dimensions: 70 x 100 x 115mm (H x W x D)
Installation: 35mm DIN rail or 4mm (3/16”) screws
The specifications are subject to change without notice.
Type Selection Table
Type Terminals 11-12 Terminals 1-3 Terminals 2-3
T7900.0010 24V DC / AC
T7900.0030 250V AC
Other supply voltages are available on request.
Accessories
G0100.0010 Optional Programming Kit for PC configuration
01-2017