CBLé System Guidebook 59
About the Temperature Probe
The TI temperature probe uses a thermistor to measure temperature.
The units are in degrees Celsius. The thermistor is a variable resistor
whose resistance decreases nonlinearly with increasing temperature.
The best-fit approximation to this nonlinear characteristic is the
Steinhart-Hart equation (refer to the table below).
At 25°C, the resistance is 20 Kohms and the sensitivity is approximately
4.3% per °C. The CBL measures the thermistor as a resistance. The
AutoIDENT
resistor contained in the probe causes the CBL software to
automatically convert the measured resistance to °C. The temperature
probe is sensitive between L20°C to +125°C. It is water resistant, but do
not leave it in water for more than 24 hours.
Temperature Probe Specifications
Channels Connects to
CH1
,
CH2
,
CH3
(analog
channels)
Current drain 0.5 mA max.
Temperature range L20 to 125°C
Chemical tolerance Tap water, salt water, and some chemicals.
(Refer to “Temperature Probe and
Chemical Tolerance” on the next page.)
Conversion equation
(Steinhart-Hart model)
Coefficients
T = [K
+ K
1
(ln 1000R) +
K
2
(ln 1000R)
3
]
-
1
L273.15
where T is temperature in °C and R is the
measured resistance in KJ.
K
= 1.02119
E
-3
K
1
= 2.22468
E
-4
K
2
= 1.33342
E
-7
Accuracy ±2.50°C from L20°C to 0°C
±1.25°C from 1°C to 85°C
±2.50°C from 86°C to 125°C
Pins used 2 Ground
3 Vres
4
AutoIDENT
resistor
6 Signal
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