PT100 and 4-20ma

[aeviaanah]

I have long distance (30') runs from PT100 probe to amifier at BC panel. I heard a while back that a 4-20ma signal may be better. Looking to understand if using 4-20ma is best for this scenario ad well as how I can achieve this. Thanks

 

[doug293cz]

To use 4-20ma signalling, you need a signal processor close to the point of the measurement. The signal processor needs to convert the thermocouple or PT100 reading into the analog current signal. I think you will find this option to be much more trouble than it is worth.

Brew on

 

[Vale71]

You'll need something like this.
It requires its own 24V power source. With 30' feet of cable it's questionable whether you really need this or not. For cable runs of several hundreds of feet on the other hand it's definitely a must.

 

[aeviaanah]

Ok thanks guys

 

[aeviaanah]

Thinking about making this purchase from Alibaba Express. It's a bit odd to me shipping is so cheap and I'm questioning if this is 100M or not.

What you guys think?

#Aliexpress US $69.16 9%OFF | PT100 compensating lead wire / Four-core silver shield high temperature wire 3*0.15 / 4*0.15 wire for PT100A sensor
https://a.aliexpress.com/_dVSL81G

 

[doug293cz]

Thinking about making this purchase from Alibaba Express. It's a bit odd to me shipping is so cheap and I'm questioning if this is 100M or not.

What you guys think?

#Aliexpress US $69.16 9%OFF | PT100 compensating lead wire / Four-core silver shield high temperature wire 3*0.15 / 4*0.15 wire for PT100A sensor
https://a.aliexpress.com/_dVSL81G

Looks reasonable. Note that the offer both 3 wire and 4 wire versions.

Brew on

 

[aeviaanah]

Looks reasonable. Note that the offer both 3 wire and 4 wire versions.

Brew on

All of my PT100s are wired 3-wire although there are (4) terminals on the amplifiers I use. Should I be running 4-wire for any reason? When would one run 4-wire as opposed to 3?

 

[doug293cz]

What do you mean by "amplifier"? Most of the devices that are commonly used in homebrew control panels (PID's & EZBoils) are set up for three wire PT100 RTD's, although I think I have seen some that will accept 4 wire's.

Brew on

 

[BrunDog]

RTD is relatively low impedance... should be ok with 30' run. I would use shielded cable, tied to ground back at the panel.