Choosing a Temperature Sensor to work with PLC

Is thers a temperature sensor that connects directly to PLC.

Yes.

Most PLCs have RTD and T/C (thermocouple) input cards available that can connect directly to the PLC. For temperature ranges RTDs are easier to implement. For very high temperature ranges T/Cs are preferred.

If you have only a few temperature sensors or if you have to connect over a long distance it may be more economical and more accurate to use a temperature temperature sensor with a transmitter that sends a 4-20 mA signal to the PLC and connects to a standard analog input card.

Or, if you need to connect several RTD or thermocouples from a long distance, or if you have a PLC that has very expensive or non-existant analog input cards, you could use something that took the inputs and communicated them over a serial connection (or an Ethernet link) to the PLC...

Omega makes a great temperature sensor that has a 4-20 output. These look like a standard RTD, but the transmitter is built into the connector. They are well built, and accurate. These are great for tanks, vats, and piped systems.

There are also infrared sensors that provide 4-20. These are more expensive, but work great for non-contact situations. I used these to monitor the temperature of parts leaving an oven. I used this input to control the cooling section of the oven.

The options can be staggering. Try Http://Omega.com for product finders guides.