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3 Operating the TED4015 Series
15
3.1.3 Connecting a Temperature Sensor
The temperature controller in the TED4015 can be used with the following temperature
sensors: NTC thermistor, AD590, AD592, LM35, LM335, LM235, LM135, PT100, and PT1000.
The setting and measurement range of thermistors is 100 Ω to 100 kΩ (Low range) and 1 kΩ to
1 MΩ (High range). The displayed temperature of the used thermistor and the temperature set
point range are dependent on the sensor parameters.
If one of the other sensor types is used, the measurement range is -55°C to +150°C.
The actual control range and the accuracy of the displayed temperature depend on the operat-
ing range and the tolerance of the used sensor, and on the individual thermal setup.
The temperature sensor is connected to the 17W2 DSUB jack "TEC OUTPUT" (R16,
). The wiring depends on the used sensor type.
Attention
Do not connect any sensor pin to the TEC element pins A1 or A2, otherwise the connected
components may be damaged!
3.1.3.1 NTC Thermistor
Connecting a
thermistor
The thermistor is connected between pin 3 and pin 4 of the 17W2 mixed DSUB
jack (R16,
Operating elements at the rear panel
). The polarity is unimportant if the
thermistor is ungrounded. If one pin of the thermistor is grounded (for example in a
laser module), this pin must be connected to pin 3.
With a thermistor as temperature sensor, the resistance can be converted into the
temperature by using the Exponential or the Steinhart-Hart calculation method.
Using the exponential method, the relation between temperature and NTC ther-
mistor resistance (and vice versa) is approximated by the formulas:
with:
R
0
- Thermistor nominal resistance at temperature T0
T
0
- Nominal temperature (usually 298.15 K = 25° C)
β - Thermistor constant (sensitivity index, B value)
T - temperature in K (Kelvin)
For R
0
, T
0
and β please refer to the data sheet of the thermistor.
Using linearization series resistors, the thermistor measurement circuit of the instrument is op-
timized for best resolution with R
0
= 10 k
W
(Low Range) and R
0
= 100 k
W
(High Range). Ther-
mistors with other R
0
values can be used at the expense of a degraded resolution, depending
on the actual sensor resistance.
If the exponential method parameters given in the thermistor data sheet are stored in the
TED4015 setup, the thermistor temperature can be shown on the display.
A further way of approximating the relation between temperature and thermistor resistance is
the method according to Steinhart-Hart, described by the formula
