How to connect thermocouple to a PLC input module

[danw]

Where's the excitation current coming from to read the IR drop across the resistance?

 

[Rashwan_Mzhr]

There are only two terminals in the sensor box. I will attach pic for it

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[Rashwan_Mzhr]

What I pan to do is connecting the two terminals that the sensor has directly to the analog input device (to +inCh0 and -inCh0 ), After that I will try to do normalization and scaling.

 

[Rashwan_Mzhr]

Where's the excitation current coming from to read the IR drop across the resistance?

It should come from the analog input device. Am I right ?

 

[nehpets]

As bit bucket says, none of the sensors appear to be Thermocouples. Can you tell us which one you have (model no.)

Steve

 

[BobB]

Thermistors - AAARGH! More inaccurate than thermocouples! Also harder to scale. Forget it and buy a 3 wire RTD and input module. 2 wire are also inaccurate and there is no resistance compensation wire. One has to be careful with thermocouples as well as the output will vary along the distance of a cable as it passes through different temperatures. Thermocouple compensation cable must be used. Additionally any terminals used along the way should be of the same material as the thermocouple wires - this means different terminals for the 2 wires.

 

[Rashwan_Mzhr]

As bit bucket says, none of the sensors appear to be Thermocouples. Can you tell us which one you have (model no.)

It's 0-45

 

[nehpets]

Oh dear, it's not going to be as easy as you think.
First we need to know the PLC type, basically I'm not sure of any mainstream PLC's that accept a direct thermistor input, analogue cards generally accept 0-5V, 0-10V, 0-20mA or 4-20mA inputs.
I would therefore suggest that you need a signal conditioner or amplifier that accepts thermistor inputs and converts it to one of the analogue cards input signal levels.
Others on this forum may have another solution.

Steve

 

[bright676]

All I did is use a J or K thermocouple, attached it to a 4-20Ma Thermocouple transmitter and from there to my analog input on my SLC-500.

Then I used the SCP instruction to send it to a N file which was the reading in Celsius so I had to add a couple of rungs to convert that to Fahrenheit and sent it to another N file which I am using for the tag address on my HMI.

I have been using this at home for the past 2 years with out issues.

 

[danw]

It should come from the analog input device. Am I right ?

Yes, but only an RTD card or an RTD transmitter is designed to provide a constant current excitation. DC volt AI cards do not have excitation sources.

 

[realolman]

Rashwan Mzhr ...Please use this before I have a stroke


The LM34 device does not require any external calibration or trimming to provide
typical accuracies of ±1/2°F at room temperature and ±1-1⁄2°F over a full −50°F to 300°F temperature range.

Operates From 5 to 30 Volts ........PLC analog range
Less Than 90-μA Current Drain



$2.30 .......cheaper on ebay

http://www.newark.com/texas-instruments/lm34dz-nopb/temperature-sensor-1f-to-92-3/dp/41K4759?mckv=s1pV1qEmc|pcrid|57087234021|plid|&CMP=KNC-GPLA?gross_price=



easy to use:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.ti.com%2Flit%2Fds%2Fsymlink%2Flm34.pdf&ei=g6IzVZanCcSzggTTw4CgAg&usg=AFQjCNGV4NvgDOVcwjl9a-zCnWiDRuAnfQ

 

[shooter]

what is resistance you measure in the connection box?

 

[NetNathan]

Rashwan Mzhr ...Please use this before I have a stroke


The LM34 device does not require any external calibration or trimming to provide
typical accuracies of ±1/2°F at room temperature and ±1-1⁄2°F over a full −50°F to 300°F temperature range.

Operates From 5 to 30 Volts ........PLC analog range
Less Than 90-μA Current Drain



$2.30 .......cheaper on ebay

http://www.newark.com/texas-instruments/lm34dz-nopb/temperature-sensor-1f-to-92-3/dp/41K4759?mckv=s1pV1qEmc|pcrid|57087234021|plid|&CMP=KNC-GPLA?gross_price=



easy to use:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.ti.com%2Flit%2Fds%2Fsymlink%2Flm34.pdf&ei=g6IzVZanCcSzggTTw4CgAg&usg=AFQjCNGV4NvgDOVcwjl9a-zCnWiDRuAnfQ

Nice device....I will have to test one of these.

 

[Rashwan_Mzhr]

Rashwan Mzhr ...Please use this before I have a stroke


The LM34 device does not require any external calibration or trimming to provide
typical accuracies of ±1/2°F at room temperature and ±1-1⁄2°F over a full −50°F to 300°F temperature range.

Operates From 5 to 30 Volts ........PLC analog range
Less Than 90-μA Current Drain



$2.30 .......cheaper on ebay

http://www.newark.com/texas-instruments/lm34dz-nopb/temperature-sensor-1f-to-92-3/dp/41K4759?mckv=s1pV1qEmc|pcrid|57087234021|plid|&CMP=KNC-GPLA?gross_price=



easy to use:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.ti.com%2Flit%2Fds%2Fsymlink%2Flm34.pdf&ei=g6IzVZanCcSzggTTw4CgAg&usg=AFQjCNGV4NvgDOVcwjl9a-zCnWiDRuAnfQ

The PLC range that I have 0 to 10 V. so, I guess the device that you suggest doesn't work. Thanks

 

[Rashwan_Mzhr]

what is resistance you measure in the connection box?

Its about 10.50 K OHM. It changes quickly when I touch it.