RS485 Temperature & Humidity Sensor (SEN0438)

Support Product Questions
1

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This is a high-precision industrial-grade RS485 temperature and humidity sensor. It uses high-quality digital integrated transducer and reliable digital processing…

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2

How does this device report temperatures < 0 degrees C? The temperature register is just two bytes. The examples given in the manual do not show any readings less than 0 degrees. Is there a sign bit there too that is not mentioned in the maual?

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3

Hi John,
Great question and a very deep rabbit hole to get into.
I am not entirely sure but there is a good chance the hex in the instruction manual is in 2’s compliment which can be negative. The example that is given works with this theory.

4

If Jack is correct and its 2’s complement representation here is an 8 bit example:

+127 0111 1111
+126 0111 1110
. . .
+2 0000 0010
+1 0000 0001
+0 0000 0000
-1 1000 0001
-2 1000 0010
. . .
-126 1111 1110
-127 1111 1111
-128 1000 0000

Except this device is using 16 bits according to the manual.

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5

Spot on Stephen.

Here’s a converter I have found that will help others

6

Thanks for the info Jack and Stephen