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Old May 23rd, 2018, 06:59 PM   #1
QasimFSH
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Using thermocouple with TM221CE16R

HI All,

I have to use thermocouple (sine the give voltage as output), and I have two analog inputs in my TM221CE16R, which are voltage dependent (0-10v, with LSB of 10mV). How can I do that? I guess I cant do this directly, does anyone know of any reliable, but a bit cheap amplifiers for Thermocouples? The other option is to but the extra cartridge for thermocouples by Schneider Electric.

Any suggestion?

Thanks.
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Old May 23rd, 2018, 08:30 PM   #2
willxfmr
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https://www.omega.com
They can turn just about any signal you have to any signal you want.


Bubba.
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Old May 23rd, 2018, 09:00 PM   #3
QasimFSH
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Quote:
Originally Posted by willxfmr View Post
https://www.omega.com
They can turn just about any signal you have to any signal you want.


Bubba.
Thanks mate, but I can get the extra cartridge for $159..
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Old May 23rd, 2018, 09:17 PM   #4
danw
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Look at how little voltage a thermocouple produces (approximate values):

Type K 0 to 1200 Deg C = 0 to 48.8mV, 1 Deg C change ranges from approx 0.039mV to 0.034mV
Type J 0 to 1200 Deg C = 0 to 69.5mV, 1 Deg C change ranges from approx 0.050mV to 0.057mV
Type T 0 to 400 Deg C = 0 to 20.8mV, 1 Deg C change ranges from approx 0.039mV to 0.062mV

A 0 to 10Vdc input does not have enough resolution to handle is too such small changes as 0.034mV (0.000034V)/deg. That's 10.0V/0.000034 = 294,117 parts of resolution = 100 0111 1100 1110 0110 which would require a 19 bit A/D converter to resolve a 1 degree C change in K type thermocouple, assuming no noise

The suggested alternative is to use a temperature transmitter which produces a 0-10Vdc output proportional to a scaled temperature input.

Be alert to the fact that a configuration tool for scaling the temperature (0-100 Deg? 200-400 Deg C? 0-1500 Deg C?) over the range of the output (0-10V) requires some means - keyboard and display, PC with Modem and software, HART communicator, all of which cost something.

If you're not will to spend money on a configuration tool, look for a vendor that sells a transmitter pre-configured to the range you need, or who will configure it for you for some nominal fee.

Also be aware that a grounded thermocouple with a non-isolated transmitter can create a ground loop the looks like a tempeature offset.

My suggestion is to always buy 'ungrounded' thermocouple assembly.
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Old May 24th, 2018, 06:52 PM   #5
QasimFSH
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Quote:
Originally Posted by danw View Post
Look at how little voltage a thermocouple produces (approximate values):

Type K 0 to 1200 Deg C = 0 to 48.8mV, 1 Deg C change ranges from approx 0.039mV to 0.034mV
Type J 0 to 1200 Deg C = 0 to 69.5mV, 1 Deg C change ranges from approx 0.050mV to 0.057mV
Type T 0 to 400 Deg C = 0 to 20.8mV, 1 Deg C change ranges from approx 0.039mV to 0.062mV

A 0 to 10Vdc input does not have enough resolution to handle is too such small changes as 0.034mV (0.000034V)/deg. That's 10.0V/0.000034 = 294,117 parts of resolution = 100 0111 1100 1110 0110 which would require a 19 bit A/D converter to resolve a 1 degree C change in K type thermocouple, assuming no noise

The suggested alternative is to use a temperature transmitter which produces a 0-10Vdc output proportional to a scaled temperature input.

Be alert to the fact that a configuration tool for scaling the temperature (0-100 Deg? 200-400 Deg C? 0-1500 Deg C?) over the range of the output (0-10V) requires some means - keyboard and display, PC with Modem and software, HART communicator, all of which cost something.

If you're not will to spend money on a configuration tool, look for a vendor that sells a transmitter pre-configured to the range you need, or who will configure it for you for some nominal fee.

Also be aware that a grounded thermocouple with a non-isolated transmitter can create a ground loop the looks like a tempeature offset.

My suggestion is to always buy 'ungrounded' thermocouple assembly.
you are righ on spot..I feel that using an RTD or thermocouple with the temperature input module(which I have to but extra) of my PLC will be the best option.
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