Wavelength Electronics WTC32ND, Datasheet And Operating Manual

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WTC32ND TEMPERATURE CONTROLLER
RESISTIVE HEATER TEMPERATURE CONTROL
The WTC32ND can operate resistive heaters by disabling
the cooling output current. When using Resistive Heaters
with NTC thermistors, connect LIMA (Pin 3) to GND (Pin 13)
with a 1.5 kΩ resistor.
Connect LIMB (Pin 4) to GND (Pin 13) with a 1.5 kΩ
resistor when using RTDs, LM335 type, and AD590 type
temperature sensors with a resistive heater.
DETERMINE I
BIAS
The resistance of your sensor in conjunction with the sensor
bias current must produce a setpoint voltage between
0.25 V and (V
DD
- 2 V) in order to be used in the control
loop. Equation 6 shows the relationship.
• Connect a resistor R
BIAS
between BIAS (Pin 10) and V
DD
(Pin 1) to set the sensor bias current.
• The LM335 always uses a 10 mA bias current (see
Table 8 for conversion equation).
Equation 6. Calculating I
BIAS
I
BIAS
=
V
SET
Sensor Resistance
SET THE SENSOR BIAS CURRENT AND SENSOR
GAIN RESISTORS
Table 10 lists the suggested resistor values for R
BIAS
and R
G
for various sensors and resistance values.
Equation 7 demonstrates how to calculate a value of R
BIAS
given a desired sensor bias current, I
BIAS
.
Equation 7. Calculating R
BIAS
R
BIAS
=
2
[ Ω ]
I
BIAS
Table 10. Resistor Value and Resistance Range
SENSOR TYPE I
BIAS
R
BIAS
SENSOR
GAIN
R
G
2.252 kΩ Thermistor 1 mA 2 kΩ 1 Open
5 kΩ Thermistor 200 µA 10 kΩ 1 Open
10 kΩ Thermistor 100 µA 20 kΩ 1 Open
20 kΩ Thermistor 50 µA 40 kΩ 1 Open
50 kΩ Thermistor 20 µA 100 kΩ 1 Open
100 kΩ Thermistor 10 µA 200 kΩ 1 Open
500 kΩ Thermistor 2 µA 1 MΩ 1 Open
100 Ω Platinum
RTD
1 mA 2 kΩ 10 Short or
100 Ω *
1 kΩ Platinum RTD 1 mA 2 kΩ 1 Open
LM335 1 mA 2 kΩ 1 Open
R
GAIN
AD590 10 kΩ Open 1 Open
* Sensor Gain with 100 Ω is exactly 10. Sensor Gain shorted is 10.09.
When using RTDs, signal can be very low. The sensor signal
applied to S+ (Pin 9) can be amplified up to a factor of 10 by
inserting a resistor, R
G
, between SG (Pin 8) and GND (Pin 13).
Connect SG (Pin 8) directly to GND (Pin 13) for a sensor gain
of 10.09. The lower the value of R
G
, the more gain applied to
the sensor signal.
Equation 8 demonstrates how to calculate a value for R
G
given a desired sensor gain.
Equation 8. Calculating R
G
R
G
=
(
90,900
- 10,000
)
[ Ω ]
(G
SENSOR
- 1)