Humidty Sensor Spikes

[stevendt]

Hi,

I have a Hobby Boards Temp/Humidity sensor which works OK most of the time but very occasionally will randomly spike up to 100% for one reading. Has anyone else seen anything similar ? I'm using software that I wrote myself but the 1-wire routines are pretty much based on Brian Lane's Digitemp code using the "C" Library.

The sensor is mult-dropped with half a dozen temperature sensors and driven from a HB 6 port Hub.

Any ideas folks ?
Bad sensor ?
Bad network ? (Cat 6 cable ~ 20m on this hub port)
"Noise" on the network ?
Other ideas ?

regards
Dave

 

[ericvic]

I have seen random spikes in some software I have been working on but I have been unable to figure out exactly what is causing it. I just filter out changes that are too large to get rid of the bad data.

Eric

Hi,

I have a Hobby Boards Temp/Humidity sensor which works OK most of the time but very occasionally will randomly spike up to 100% for one reading. Has anyone else seen anything similar ? I'm using software that I wrote myself but the 1-wire routines are pretty much based on Brian Lane's Digitemp code using the "C" Library.

The sensor is mult-dropped with half a dozen temperature sensors and driven from a HB 6 port Hub.

Any ideas folks ?
Bad sensor ?
Bad network ? (Cat 6 cable ~ 20m on this hub port)
"Noise" on the network ?
Other ideas ?

regards
Dave

 

[sda]

Make sure you're not reading the memory until after Convert V is completed, issue reads until you get a 1. After you do the Recall Memory validate the CRC. This is all described in the DS2438 data sheet. Look into what's actually being returned as the voltage before its converted to a percentage. The HIH-3610 should be reading between 2v and 3v for normal conditions. See the HIH-3610 datasheet for a chart. If you verify the code is working correctly and you're actually getting readings above 4v, then there might be a transient glitch in the hardware. Another possibilty is the routine that takes the voltage and converts from voltage to RH%, usually adjusting for temperature, is broken under some conditions.

 

[stevendt]

Thanks Eric,

sounds like it's not unique to my system then, I think that the easiest thing will be to do the same as you and filter out the spikes with software,

regards
Dave

I have seen random spikes in some software I have been working on but I have been unable to figure out exactly what is causing it. I just filter out changes that are too large to get rid of the bad data.

Eric

Hi,

I have a Hobby Boards Temp/Humidity sensor which works OK most of the time but very occasionally will randomly spike up to 100% for one reading. Has anyone else seen anything similar ? I'm using software that I wrote myself but the 1-wire routines are pretty much based on Brian Lane's Digitemp code using the "C" Library.

The sensor is mult-dropped with half a dozen temperature sensors and driven from a HB 6 port Hub.

Any ideas folks ?
Bad sensor ?
Bad network ? (Cat 6 cable ~ 20m on this hub port)
"Noise" on the network ?
Other ideas ?

regards
Dave

 

[stevendt]

Hi,

thanks for the tips. I'll add some extra debug lines to the code and see if I get any ideas that way. Short term fix will be to filter out the bad values as suggested by Eric

regards
Dave

Make sure you're not reading the memory until after Convert V is completed, issue reads until you get a 1. After you do the Recall Memory validate the CRC. This is all described in the DS2438 data sheet. Look into what's actually being returned as the voltage before its converted to a percentage. The HIH-3610 should be reading between 2v and 3v for normal conditions. See the HIH-3610 datasheet for a chart. If you verify the code is working correctly and you're actually getting readings above 4v, then there might be a transient glitch in the hardware. Another possibilty is the routine that takes the voltage and converts from voltage to RH%, usually adjusting for temperature, is broken under some conditions.