Keithley TEC SourceMeter 2510, Service Manual, Page: 67 / 120

4-10 Troubleshooting Models 2510 and 2510-AT
Measurement circuits
Signal conditioning for the external temperature sensor is provided by U124, U149, and
associated components. Voltage and current feedback signals from the TEC output terminals
are developed by U147 and U151.
The conditioned temperature sensor, voltage, and current, feedback signals are fed to the
multiplexer IC, U142, that switches among the signals during the various phases of the mea-
surement cycle. The output of the mux is fed to the A/D converter for conversion to digital
data. Additional signals switched by the mux during the measurement cycle include a reference
voltage, reference temperature, internal circuit board temperature signal, and an in15V
measurement.
Sensor conditioning
Figure 4-6 shows a simplified schematic of the sensor conditioning circuits. In this example,
measurement using a 10k
Ω
thermistor is assumed. Sensor conditioning for other thermistor
ranges and sensor types is similar.
+15V
DUT
GND +
GND -
THPFBK
2 Wire
2 Wire
MEAS_10K
SHUNT_10K
10K 100K
Figure 4-6
Sensor conditioning
for 10k
Ω
thermistor
2510-902-01 (E - Mar 2010)(Service).book Page 10 Tuesday, March 16, 2010 1:04 PM