Wavelength Electronics LDTC0520, Техническое описание и руководство по эксплуатации

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LDTC0520 / LDTC1020 LASER DIODE AND TEMPERATURE CONTROLLER
SENSORS OTHER THAN A 10 k
Ω
THERMISTOR
The LDTCxx20 is factory‑configured to bias a 10 kΩ
thermistor with 100 µA current, but with simple modifications
other sensors can be used. The instructions for making the
changes (sensor bias current resistor and gain resistor)
are included here, and are recommended for users with
experience soldering surface mounted components. These
modifications can be made at the factory, as well.
Set the Sensor Bias Current Resistor
To change the sensor bias current (I
BIAS
), the 1206‑sized
surface mount R
BIAS
resistor must be replaced. Table 5
indicates the proper R
BIAS
and R
S
values, and Figure 20
shows their location.
I
BIAS
can be adjusted to other values based on the value of
R
BIAS
, according to the relation:
R
BIAS
=
2
(3)
I
BIAS
The 100 Ω sensor gain resistor (R
S
) may need to be added
to two pins that protrude from the top of the circuit board
(read the Adjust Sensor Gain section below).
Table 5. R
BIAS
and R
S
for Alternate Temperature Sensors
SENSOR TYPE
R
BIAS
I
BIAS
R
S
GAIN
2.25 kΩ Thermistor 2 kΩ 1 mA Open 1
5 kΩ Thermistor 10 kΩ 200 µA Open 1
10 kΩ Thermistor
Default
20 kΩ 100 µA Open 1
20 kΩ Thermistor 40 kΩ 50 µA Open 1
50 kΩ Thermistor 100 kΩ 20 µA Open 1
100 kΩ Thermistor 200 kΩ 10 µA Open 1
500 kΩ Thermistor 1 MΩ 2 µA Open 1
100 Ω Pt RTD 2 kΩ 1 mA 100 Ω 10
1 kΩ Pt RTD 2 kΩ 1 mA Open 1
LM335 2 kΩ 1 mA Open 1
AD590 Open – Open 1
RBias
Sensor Gain Resistor
Rs = 100 Ω
Figure 20. Location of R
BIAS
and R
S
— Rev C only
RBias
Sensor Gain Resistor
Rs = 100 Ω
Figure 21. Location of R
BIAS
and R
S
— Rev A & B only
Adjust Sensor Gain
If the desired temperature setpoint results in a sensor voltage
below 250 mV, the temperature controller may not achieve
high levels of precision and stability. In such cases the
sensor voltage can be amplified by a factor of 10 by adding
a 100 Ω sensor gain resistor (R
S
) as shown in Figure 20 .
Adding the sensor gain resistor to amplify the sensor
voltage requires amplifying the setpoint voltage, as well. For
example, in a system using a 100 Ω RTD biased at 1 mA, the
actual sensor voltage is 110 mV at 25ºC. If the R
S
resistor
is added, the controller will amplify the voltage internally to
1.10 V. The temperature setpoint value, therefore, will also
have to be 1.10 V.
Use the LM335
To use an LM335 sensor refer to
Table 4
for wiring
instructions specific to your application. Refer to the sensor
datasheet for the external resistor value and temperature
transfer function. Change the R
BIAS
resistor to 2 kΩ.
Use the AD590
To use an AD590 sensor refer to Table 4 for wiring
instructions specific to your application. Refer to the sensor
datasheet for supply voltage requirements and temperature
transfer function. Remove R
BIAS
from the LDTC.