Hi Robert,
on my Dew-Controller is a differenc between the three DS18B20 and the DHT22 from about 0.8 C°.
Is this a Problem for the Controller?
All three DS18B20 shows eg. 20 C° and the DHT22 schows 20.8 C°.
Should or can i calibrate this?
Best regards
Andreas
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi Andreas
I assume when you hold the probe end in you hand the temperature rises? That the probes are working?
Yes, there is a difference, mechanically between each probe in terms of thermal characteristics due to variations in mounting the sensor and its conductivity to the outer metal part of the probe, the variations in cable length and wire diameter, the variations in resistor values etc.
I would be very surprised if they were all the same.
At the end of the day even a degree or so variation between each other will not really affect the operation of the controller.
What I normally do is pick the average of the temperature probes and set the bias of each so that it meets the average. I dont bother to compensate for the DHT22 as that is not a reliable standard anyhow. I prefer to use the HTU21D sensor as I have found it to be slightly more accurate.
But realize that there variations all over the place, depending on where the dew controller is located, the sensors exposure and orientation to the air etc etc, It is not a laboratory instrument, ball park is good enough as the various algorithms will more than compensate for these variances.
Regards
Robert
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi Robert,
on my Dew-Controller is a differenc between the three DS18B20 and the DHT22 from about 0.8 C°.
Is this a Problem for the Controller?
All three DS18B20 shows eg. 20 C° and the DHT22 schows 20.8 C°.
Should or can i calibrate this?
Best regards
Andreas
Hi Andreas
I assume when you hold the probe end in you hand the temperature rises? That the probes are working?
Yes, there is a difference, mechanically between each probe in terms of thermal characteristics due to variations in mounting the sensor and its conductivity to the outer metal part of the probe, the variations in cable length and wire diameter, the variations in resistor values etc.
I would be very surprised if they were all the same.
At the end of the day even a degree or so variation between each other will not really affect the operation of the controller.
What I normally do is pick the average of the temperature probes and set the bias of each so that it meets the average. I dont bother to compensate for the DHT22 as that is not a reliable standard anyhow. I prefer to use the HTU21D sensor as I have found it to be slightly more accurate.
But realize that there variations all over the place, depending on where the dew controller is located, the sensors exposure and orientation to the air etc etc, It is not a laboratory instrument, ball park is good enough as the various algorithms will more than compensate for these variances.
Regards
Robert