Linear Technology ANALOG DEVICES DC2608 Manual page 16

DEMO MANUAL DC2608
HARDWARE SETUP
DC2214 DEDICATED THERMISTOR BOARD
The DC2214 dedicated thermistor board includes several
circuits (see Figure 15) to demonstrate the flexibility, ac-
curacy, and low noise features of the LTC2986-1 thermistor
sensor modes.
The DC2214 provides a 10kΩ ±0.1% 15ppm/°C sense
resistor on channels 1 and 2 which is shared with all of
the thermistor sensor circuits on this board (see schematic
diagram Figure 16 and corresponding software configura-
tion Figure 17). The measured value of this sense resistor
is stored in an on-board EEPROM which the LTC2986-1
demo software can read and use to configure the sense
resistor value.
To demonstrate the low system noise of the LTC2986-
1 the dedicated thermistor board provides a 25°C 10k
thermistor simulator (10kΩ ±0.1% 15ppm/°C) on chan-
nels 2-4 configured as a differential sensor. In addition to
this the user may use this circuit to demonstrate how the
rotated mode eliminates measurement error introduced by
parasitic thermocouples. To facilitate this demonstration
the DC2214 provides an external thermocouple interface
which acts as a parasitic thermocouple.
To see the effects of parasitic thermocouples on non-
rotated measurement modes, first measure the on-board
25°C 10k thermistor simulator in a no-rotation/sharing
configuration and see the measurement error as the
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thermocouple's temperature changes. To see the benefit
of the rotated measurement mode, switch to the rotation/
sharing configuration and see the errors introduced by the
parasitic thermocouple disappear (the effects are more
significant with lower excitation current).
The DC2214 also includes a 499kΩ (0.1% 15ppm/°C)
thermistor simulator on channels 9 and 10. Ideally, this
resistor simulates –30.59°C for a 44008 (30k) thermistor
and –51.94°C for a 44006 (10k) thermistor. Note, the 10k
thermistor reports the temperature, but also indicates a
soft fault since the temperature is below the thermistor's
specified minimum temperature.
In addition to the fixed value thermistor simulators, there
is a variable resistor thermistor simulator as well. This
circuit can be used to demonstrate the range of the various
LTC2986-1 thermistor sensor modes as well as demon-
strate the fault detection capabilities of the LTC2986-1.
If the user wishes to connect an external thermistor to the
daughter board, a 2-position terminal block is provided.
The user may connect any of the LTC2986-1 supported
thermistors as well as custom thermistors to the DC2618
demo board through this interface. To demonstrate the
accuracy of the LTC2986-1, the user may connect external
resistance standards to this interface.
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