Reading RTD''s
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Posts: 46,084
The problem with interference arouse from using Analog Devices AD595. This
is supposed to read the thermocouple, Condition it, linearize, and
Compensate for the cold junction, then output 10mv per degree Celsius. The
whole thing works great in my workshop, but I take it onsite and I get a odd
spiking signal. It shows fluctuations up and down of 500 or more degrees. It
almost looks like it has a heart beat... The only thing that is different is
the location. I am running it a max length of 75 feet. With experimentation
I have found the interference occurs when I extend the length beyond 10
feet. I am also using K type thermocouples with K type thermocouple
extensions. I have also tried tyroid coils, capacitors, and resistors. The
capacitors and resisters helped, but changed the linearity of the output
from the chip. It need to be accurate to about 1 degree Celcius or less, as
stipulated be the government!
Original Message
From: Dave Mucha <davemucha@j...> [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Xk7AQip7UUyItKDjp4FFapbWG5vMi52wC8mQuWJfLtN_EJ0t8aHBmmoTywSZL8meDHWWxKysPkIiHi1b]davemucha@j...[/url
Sent: Sunday, January 26, 2003 11:12 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Reading RTD's
I'm not sure of the reference to the distance of the run and the
airport interference.
Thermocouples work on a simple bi-metal principal the asserts that
dissimilar metals joined will product a voltage that varies with
temperature. the voltage is low, very low.
Understand that dis-similar metals is the key phrase. copper, lead,
tin, AND the stuff your thermocouple is made of are all dissimilar.
That means ANY and EVERY junction can act as a sensing point. the
terminals on your device may be a reference joint. you cannot use
any extention of thermocouple wire, it MUST be an uninterupted home
run all the way from the process to your ADC.
errors can be eleminated by a cold junction reference and calibration.
Curcuit board temperature monitoring also helps to reduce errors.
You might conssidder an automobile exhause gas sensor as well and an
RTD.
If you get a transmitter, you will gain a complete circuit and have a
voltage or current output.
Also, you may need to look at thermowell's. these are the metal
deviced used to house the sensor to the actual sensor does not come
in contact to the gasses.
Dave
--- In basicstamps@yahoogroups.com, "Phillip Kocmoud" <pkocmoud@h...>
wrote:
> Can anyone kick me in the right direction? I am interested in
monitoring the
> temperature of an industrial oven. The monitored temperature is
between 0
> degrees Celsius and 100 degrees Celsius. I have attempted to use
> thermocouples, but the distance of the run and its location is very
close to
> a major airport, I cannot dampen the interference. I think RTD's
will fill
> my bill, but I am unable to find practical information for
integrating them.
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is supposed to read the thermocouple, Condition it, linearize, and
Compensate for the cold junction, then output 10mv per degree Celsius. The
whole thing works great in my workshop, but I take it onsite and I get a odd
spiking signal. It shows fluctuations up and down of 500 or more degrees. It
almost looks like it has a heart beat... The only thing that is different is
the location. I am running it a max length of 75 feet. With experimentation
I have found the interference occurs when I extend the length beyond 10
feet. I am also using K type thermocouples with K type thermocouple
extensions. I have also tried tyroid coils, capacitors, and resistors. The
capacitors and resisters helped, but changed the linearity of the output
from the chip. It need to be accurate to about 1 degree Celcius or less, as
stipulated be the government!
Original Message
From: Dave Mucha <davemucha@j...> [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Xk7AQip7UUyItKDjp4FFapbWG5vMi52wC8mQuWJfLtN_EJ0t8aHBmmoTywSZL8meDHWWxKysPkIiHi1b]davemucha@j...[/url
Sent: Sunday, January 26, 2003 11:12 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Reading RTD's
I'm not sure of the reference to the distance of the run and the
airport interference.
Thermocouples work on a simple bi-metal principal the asserts that
dissimilar metals joined will product a voltage that varies with
temperature. the voltage is low, very low.
Understand that dis-similar metals is the key phrase. copper, lead,
tin, AND the stuff your thermocouple is made of are all dissimilar.
That means ANY and EVERY junction can act as a sensing point. the
terminals on your device may be a reference joint. you cannot use
any extention of thermocouple wire, it MUST be an uninterupted home
run all the way from the process to your ADC.
errors can be eleminated by a cold junction reference and calibration.
Curcuit board temperature monitoring also helps to reduce errors.
You might conssidder an automobile exhause gas sensor as well and an
RTD.
If you get a transmitter, you will gain a complete circuit and have a
voltage or current output.
Also, you may need to look at thermowell's. these are the metal
deviced used to house the sensor to the actual sensor does not come
in contact to the gasses.
Dave
--- In basicstamps@yahoogroups.com, "Phillip Kocmoud" <pkocmoud@h...>
wrote:
> Can anyone kick me in the right direction? I am interested in
monitoring the
> temperature of an industrial oven. The monitored temperature is
between 0
> degrees Celsius and 100 degrees Celsius. I have attempted to use
> thermocouples, but the distance of the run and its location is very
close to
> a major airport, I cannot dampen the interference. I think RTD's
will fill
> my bill, but I am unable to find practical information for
integrating them.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/