Measurement Computing WEB-TEMP - Manual (Page 20)

WEB-TEMP User's Guide Signal Connections
20
Four-wire, single-sensor
A four-wire measurement configuration is shown in Figure 7. The diagram on the left shows the sensor
connected to the first channel in the channel pair. The diagram on the right shows the sensor connected to the
second channel in the channel pair. The # indicates the channel number. Do not make connections to pin
marked "NC".
Figure 7. Four-wire, single RTD or thermistor sensor measurement configuration
Four-wire, two-sensor
A four-wire, two-sensor measurement configuration is shown in Figure 8. The # indicates the channel number.
Do not make connections to pin marked "NC".
Figure 8. Four-wire, two RTD or thermistor sensors measurement configuration
When configured for four-wire, two sensor mode, both sensors must be connected to obtain proper
measurements.
Semiconductor sensor measurements
Semiconductor sensors are suitable over a range of approximately -40 C to 125 C, where an accuracy of
±2 C is adequate. The temperature measurement range of a semiconductor sensor is small when compared to
thermocouples and RTDs. However, semiconductor sensors can be accurate, inexpensive and easy to interface
with other electronics for display and control.
The WEB-TEMP makes high-resolution measurements of semiconductor sensors and returns a 32-bit floating
point value in either a voltage or temperature.
Use InstaCal or the web interface to select the sensor type (LM35, TMP35 or equivalent) and the sensor input
channel to connect the sensor.
Wiring configuration
Connect a semiconductor sensor using a single-ended configuration, as shown in Figure 9. The # indicates the
channel number. Do not make connections to pins marked "NC". The WEB-TEMP also provides
+5V and GND
pins for powering the sensor, but use of this power source requires overriding the isolation between analog and
power ground by connecting AGND to GND.