Specifications

Section 4. Sensor Support
4-22
measurement and does not include errors in installation or matching the sensor
and thermocouple type to the environment being measured.
4.4.1.1 Panel Temperature
The panel temperature thermistor (Betatherm 10K3A1A) is just under the panel
in the center of the two rows of analog input terminals. It has an
interchangeability specification of 0.1 °C for temperatures between 0 and 70
°C. Below freezing and at higher temperatures, this specification is degraded.
Combined with possible errors in the completion resistor measurement and the
Steinhart and Hart equation used to calculate the temperature from resistance,
the accuracy of panel temperature is estimated at ± 0.1°C over -0 to 40°C, ±
0.3°C from -25 to 50°C, and ± 0.8°C from -55 to 85°C.
The error in the reference temperature measurement is a combination of the
error in the thermistor temperature and the difference in temperature between
the panel thermistor and the terminals the thermocouple is connected to. The
terminal strip cover should always be used when making thermocouple
measurements. It insulates the terminals from drafts and rapid fluctuations in
temperature as well as conducting heat to reduce temperature gradients. In a
typical installation where the CR1000 is in a weather proof enclosure not
subject to violent swings in temperature or uneven solar radiation loading, the
temperature difference between the terminals and the thermistor is likely to be
less than 0.2 °C.
Panel Temperature error summary
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-55 -35 -15 5 25 45 65 85
Sum of Worst Case Errors
Thermistor Tolerance
CR1000 Measurement
Completion Resistor Error
S&H Err
FIGURE 4.4-1. Panel Temperature Errors
With an external driving gradient, the temperature gradients on the input panel
can be much worse. For example, the CR1000 was placed in a controlled
temperature chamber. Thermocouples in channels at the ends and middle of
Panel Temperature ºC
Error
º
C