PLC with temp input

You could ask for a PLC with "RTD inputs".
But PLCs with RTD inputs are typical small ones intended to control a single or a few temperature control loops.

Most typical today is that the PLC gets all analog signals conditioned as 4-20mA. That means that the temperature sensor has an integral 4-20mA transmitter. There are other signal types, 0-10V, +/- 10V, 0-20mA, +/-20mA, or more, but the 'industry standard' is 4-20mA.

Also, the type and number of inputs and outputs are most often not fixed but can be configured in a modular way. A PLC with a fixed number of I/O is called a "brick". Personally I dont like brick PLCs. If you can find a brick PLC with exactly the nuber of I/O you need, it will almost certainly be a bit cheaper than a modular PLC. But then you have a less flexible PLC.

That the PLC shall be able to read an analog temperature signal surely cannot be the single requirement that shall decide which PLC brand and type you shall get. Try to define your needs more precisely. Also think long-term. What could your requirements be 5-10 years from now ?

In the US, the packaging industry is notorious for using THE absolute cheapest thermocouples, a pair of wire stuck into a sheath, with no insulating packing.

I suspect an RTD is way outside of their budget.

Dan

Most PLC units do have cards for thermocouple or RTD available.
It is pricedependent on what to choose, ranging from an arduino to a siemens or even higher.
bear in mind that the speed of the machine should be dependent of the temperature of the sealing.
and other way too.

If you are unfamiliar with PLCs (and you must be?) and you want to use a PLC to control your machine, then I'd recommend that you involve someone capable of doing both the control system design and PLC programming prior to specifying the PLC equipment that you'll implement. There are many more relevant questions that should be addressed than simply the I/O capabilities of your chosen PLC.

You didn't even mention the type of instrument that you plan to use to measure temperatures, and that is a prerequisite for specifying the appropriate PLC system I/O.

As far as price goes, you can go cheap FC-T1 ($120.00 in 2013)
Of course, that doesn't include the thermocouple or PLC.
Like, BB Says, you've got lots of questions, you probably haven't even considered.

How many temperature channels and how many total analog signals?
I like the IFM or AD transmitters with M12 connectors. You send it 24vdc, get back a nicely scaled 4-20mA from a nice RTD also available with or without a pigtail for the M12 plug which patches over to the compact transmitter.

AD temp stuff:
http://www.automationdirect.com/adc...surement/Temperature_Sensors_-a-_Transmitters

I have used their RTD for a HVAC system and a freezer with good results as long as the connection stays dry or well sealed (freezer connection was dry at first and shorted with wash cycle, HVAC install works flawlessly):

http://www.automationdirect.com/adc...00)_Sensors/Probes_(with_M12_Cable_Connection)

4-20mA is cheaper and easy to document/scale, although it does require two ends to be verified for scaling accuracy as opposed to a smart transmitter. It is only cheaper than a TC card until you want 16 temperature signals, then well spec'd thermocouples have their place. For extreme environments, or for general and detailed education, visit Omega.com and their selection utilities.

danw said:

In the US, the packaging industry is notorious for using THE absolute cheapest thermocouples, a pair of wire stuck into a sheath, with no insulating packing.

I suspect an RTD is way outside of their budget.

Dan

Click to expand...

Thats funny

All in one. Horner Electric. Available from Omega Engineering.
HE-XE105. $685.00 for 2 temp channels.


AD Temp control with RS485 Modbus. $90.00

AD PLC with RS485. $99.00

Add 24DC supply and touchscreen.

For multiple channels, you could use a DL06 with a TC module (4 channel).