DAEnetIP2
User Manual
12 Sep 2013
18.
Appendix 11. Using analog temperature sensors
18.1.
LM335Z
Figure 41. DAEnetIP2 and LM335Z
On the figure above it is shown LM335Z connection to DAEnetIP2 with several
resistors. LM335 may be assumed as zener diode it is necessary to limit the
current (that's why the 4.7K resistor is added). The biggest disadvantage of
LM335 is the high output voltage during 25°С – 3V. As DAEnetIP2 ADC works
in range of 0-3.3V, actually with directly connected LM335 it is not possible to
measure temperatures over 57°С. Moreover the output of LM335Z can exceed
3.3V and damage the ADC channel.
The easiest solution is using simple resistor divisor – 3:1 so the output voltage
during
25°С to be 1V. It is important the divisor resistance to be smaller because this
improves the ADC accuracy (but on the other hand it must be taken in mind also the
current in the sensor resistor). However the resistor divisor makes also the ADC
conversion bigger.
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