0FL-3924-001, 1998-09-18
3 (4)
User’s Manual
TAC 268TX is intended for room temperature control in
heating and/or cooling systems.
Heating and cooling is controlled by on/off control outputs.
Each control output can control up to three thermal type
actuators. When the system has a larger number of actua-
tors, auxiliary relays can be used for increasing the numbers.
Separate heating and cooling setpoints are obtained from a
neutral zone.
English
Settings (factory settings underlined)
On the casing:
Setpoint
The heating setpoint is adjusted by the knob
Range of setting: Blue - Red fields (+10 – +30 °C)
Factory setting: Mid position (+20 °C)
On the circuit board:
SPC (setpoint control)
The effect of an external control voltage. The setting
indicates the increase in the setpoint obtained for a 10 V
control voltage:
Range of settings: 0–8
Factory setting: 0
NZ (neutral zone)
Range of settings: 0 — +4 K
Factory setting: +2 K
The setting of NZ (neutral zone) gives a positive (+) value,
i.e. how much higher the cooling setpoint is in relation to
the heating setpoint (knob setting)
On/off control
Heating and cooling are controlled on/off by means of relay
outputs. The switching hysteresis is ± 0,1 °C.
A light emitting diode LED shows if the controller works in
heating mode (red colour) or works in cooling mode (green
colour)
Figure 1
Control signal
On
Off
Time
Setpoint
Remotely controlled setpoint control (SPC)
function
The controller has an SPC function, which makes it possible
to remotely control the setpoint.
The SPC signal is a control voltage between 2 and 10 V DC,
where the voltage range 2–6 V results in a decrease of the
setpoint and the range 6–10 V results in an increase. A value
of 6 V results in no change.
Figure 2 shows how the heating setpoint changes with the
SPC signal voltage and the SPC setting. The cooling setpoint
follows the heating setpoint, with a difference which is equal
to the preset neutral zone.
The SPC setting states how many degrees the setpoint is
shifted when the voltage is changed by 4 V.
Figure 2
Control voltage (V)
°C
8
4
0
–4
–8
2
4
6
8 10
SPC=0
SPC=4
SPC=8
Sensors
Normally the controller uses the built-in sensor. If necessary an
external sensor can be used. All TAC’s standard sensors with
50 kohm at 25 °C thermistor can be used.
Output
Heating
Cooling
NZ
0%
100%
Setpoint
Figure 3
INT EXT (thermistor sensor)
Internal/external sensor options:
Shorting plug in left position: internal sensor
Shorting plug in right position: external sensor
Limiting and locking the setpoint knob
The range of settings on the adjustment knob can be limited
using two movable pegs. Lock the knob by positioning the
pegs on either side of the required setting. The pegs are
shielded by the front cover.
Increased need
for cooling
Neutral zone
NZ
Shows heating mode
NZ
SPC
INT EXT
Figure 4
