Infrared Pyrometer vs. Thermocouples or RTD's

[BITS N BYTES]

We have a customer with Thermocouples and RTD's for temperature control. This temperature measurement system is not working for them as the read heads are constantly damaged, broken or not regularly maintained.
They are seeking a solution to resolve their issues. We are wondering IF an industrial infrared pyrometers would be a suitable replacement.
Has anyone used these devices? If YES then recommendations for best/reliable units and any pointers as how to implement them would be much appreciated.
We will be using an OMRON PLC to receive inputs from the infrared pyrometers and control the heaters from its outputs.

Temperature control is a new experience for us!!!

 

[g.mccormick]

What is the process? How do the existing sensors keep getting damaged?

 

[ASF]

I have used one of these with good results. 4-20mA out and apparently available with Ethernet/Profinet as well. It also has a very wide range - can be configured anywhere from -40 to +1800 degrees celcius (what the hell are you measuring at 1800C?!).

I use it to monitor frozen product at around -30C and it works well. They also have plenty of accessories available, e.g. an air purge collar to keep condensation off the lens if the area is prone to steam, etc.

 

[danw]

"Non-contact", sounds great, doesn't it?

To me, it's like wireless, it always works under the ideal conditions of a work bench in an office or lab.

And every plant I've ever been in has office/lab grade ideal conditions, doesn't it?

Have a go at it and discover all the rules, conditions, gotchas and whatnot that go with non-contact temp measurement (note the air purge option, for example; nothing like the requirement for clean dry purge air 24-7, huh?).

 

[Automation Spec]

With more information about your process you'll get better feedback. i'm currently using this in a cement kiln but it may be overkill for your customer.

https://www.processsensorsir.com/products/infrared-temperature-sensors/metis/metis-m3-product-table/

 

[tamir]

See also this :
http://www.exergen.com//industrial/industrial-products.htm

 

[nightline]

An infrared pyrometer measures the reflexion of infrared light. The amount of reflected light is strongly related to the type of material, the color of the surface and the angle of the surface to the sensor.
I've used these type of sensors to measure the realtime temperature of spinning heating drums on a foil laminator machine. These measurements where absolute not good, as they gave readings + and - 100 dgr. Celsius on a temperature of 350 dgr. Celsius.

I think that you can use them for some kind of not very acurate measurments, but if you need the same kind acurate measurment as you can do with Thermal couples or RTD's, you will not be able to perform this with pyrometers.

We had the same problem in the past with broken TC's. We had applications where we replaced the TC about every week. We switched from Farnell TC's to Thermal Electra TC's which build these TC's specially for us, and these last much longer, something in the kind of a year on the same application. They did this by using a different kind of wire.
As a TC is actualy not more than a weld of 2 different materials, there is not a lot what can go wrong with this type of sensor. So the problem is most of the time the wire which get broken by too many bending.

 

[JesperMP]

We use a lot of IR temperature sensors. The reason is that they are maintenance-free (apart from the occasional cleaning of the lens), and convenience.
IR sensors used to be expensive, now they cost next to nothing.
They work well enough for our application. 2% measuring error.
The sensors we use have a fixed setting for the measured materials reflectivity. If we used a more expensive sensor that has adjustable reflectivity I guess we could get the error down to 0.5%.

Obviously an IR-sensor is measuring the surface temperature of the material. That may be a big issue or a non-issue depending on your application.
Some materials (transparant) cannot be measured with IR sensors.
If the envireonment is very dusty, it may be necessary with purge air to keep the lens clean.

 

[redbarron55]

In a cement kiln you are usually looking for the gas temperatures and usually a thermowell and TC depending on where you are measuring.
Some places are very problematic, others not too bad.
Two devices will be required since the utility workers will occasionally break off the whole thing.
If you are measuring the exit temps of the kiln good luck, the secondary air is not so bad, but still requires two sensors for backup.

The abrasion of the thermowells would require that these be replaceable from the outside, but sometimes the buildup is such that it cannot be done anyway.
IR is difficult since it will measure the surface of the kiln and not the gas and you still need a IR transparent window that stays clean.