relative humidity, dewpoint and standard humidity

We are in the process of testing the support for DS2438 smart battery sensor.  That sensor has temperature, voltage and current sensors, three functions in one.  From users told us, many use that chip to measure humidity sensor output voltage, like sensor output from HIH4000.
 
Our question is, what would be most useful for users? RH, DewPoint, or standard humidity.  We can add PLC function to do the calculations inside firmware, if so desired.  However, we want to know the most useful features, so that they can be added first.
 
Thanks for your inputs.

The accuracy of the HIH4000 is "barely adequate", and as you get to the extremes (particularly the 100% RH end of the scale) it becomes more of a guess than an actual reading!
 
That's why I switched to AM2320 style devices, which claim significantly better accuracy in their specs, and in real life seem to produce far more believable results.
 
These devices return temperature and relative humidity, and dewpoint is just a calculation away.

The sensor family name may have been posted.
Here are the specs for the the sensor used in the SWE-3 sensor unit containing the DS2438.

AM2320 specs:
 
Humidity:
Resolution: 0.1%
Range: 0-99.9%
Accuracy @ 25 deg C  +/- 3%
Repeatability: +/- 0.1
Response times <5S
Drift <0.5 % / year
 
Claimed accuracy
<3% from 0%-99.9% RH.
<2% from 20%-70% RH
 
 
Temperature:
Resolution: 0.1 deg C (16 bits)
Accuracy +/- 0.5 deg C
Repeatability +/- 0.2 deg C
Drift: <0.1 deg C / year
 
 
Add the fact that there is zero quantization error due to ADC, no ADC drift, and the sensor doesn't take up an ADC channel, plus gives both temperature and humidity, and costs about 1/4 what a single HIH-4000 does, it's a clear winner in my books.

Wrong bus. The OP is about a 1-wire device.
 
The HIH-4031 is what the SWE-3 comes preinstalled with, as a triple sensor function, 1-wire device, with a prewired RJ-31 connector.
This unit contains the DS2438 the OP was announcing support for.
 
We did talk the vendor into making the SWE-3 available without the humidity sensor attached, though.
 
 
@CAI
I would vote for %Rh as the most common way of expressing humidity and most native to most sensors.

Ok, we will then add a PLC command to convert voltage to RH, since HIH sensors are relative humidity, it is a simple calculation.  That could be down in PLC, however, one PLC command can make it easier for higher precision calculation inside firmware. 
 
On WC8 board, there are AIP5-8 can be accessed by PLC read and write.  When DS2438 attached, first DS2438 will store its voltage reading in AIP5 and current reading in AIP6. When 2nd DS2438 sensor attached, it will store its voltage reading into AIP7 and its current reading in AIP8.  User than can use the PLC command to convert that AIP5 or AIP7 to RH reading.
 
If calculating dewpoint is desired, that will require to have a pressure sensor. There is a pressure sensor pretty cheap on eBay, that can be connected to I2C bus.

LarrylLix said:

Wrong bus. The OP is about a 1-wire device.

Click to expand...

 
The OP also said "HIH4000" which would need to connect via an analog input on *something*, regardless which bus it's on, but I take your point.
(I still prefer the improved accuracy provided by the AM2320 devices)

Do you plan  support for the Sensirion SHT1x?

There is an I2C version of that sensor. Ross had published the code for how to support that on this forum.

CAI_Support said:

There is an I2C version of that sensor. Ross had published the code for how to support that on this forum.

Click to expand...

Many thank,
 
what WC board and revision is fit for that and is the link to the contact the way you want me to request the code?
thanks

WC8 2.3.8 board would work, also WC32 board also work.   You can find Rossw from this forum then write to him. He is a very good heart person willing to help.