Product review: WIKA TR21

Let’s turn up the heat! Today we have another relevant player in the hygienic field. No, not talking about that. Or that! Talking about WIKA’s extensive experience in instrumentation. Specifically we will discuss the WIKA TR21 and see the pros and cons of this device.

Disclaimer: This product review examines only features, not performance. If you’ve used this device, feel free to share your experience in the comments.

Whatcha got there?

The TR21 miniature resistance thermometer handles applications in sanitary, food and beverage, biological, and pharmaceutical industries, helping those companies keep up the quality of their products.

A compact and simple device, the TR21 doesn’t have a display for local setup. But the sensor does integrate directly into the control system. You can also get one with a transmitter built in to convert the analog data.

Local visualization comes only with a field or panel display, but you won’t get much because of the lack of digital protocol. The TR21 with the transmitter configures using a free software from WIKA called WIKAsoft-TT PC. Sounds good, but you need the programming unit and the adapter cable. If you already have a HART handheld, you can’t use that here.

And if you want digital protocol, then check out some of WIKA’s other models, because you won’t find it here.

What can it do?

You got it – it’ll measure temperature using resistance temperature detection or RTD.  You can scale out for various measuring elements like PT100s or PT1000s.

It can measure temps from -30 to 250 degrees Celsius. However, over 85 requires protection on the transmitter. If you don’t have a built-in transmitter, then don’t worry about it. The maximum process pressure depends on the thermowell and process connection. The datasheet has a table with all the options.

For connections, it has three different options.  You can pick the TR21-A if you like flanges, TR21-B for orbital welding, or TR21-C with an integrated sterile connection.

As for insertion length, let’s use the WIKA TR21-A as an example. You can get the insertion length (U1) in 25, 50, 75, 100, 150 and 200 millimeters, and your thermowell diameter in 6 millimeters. You can see the entire configuration list here.

Courtesy of WIKA

Why should I care?

As I said in the last review, temperature changes slowly, but the sensor should detect it quickly so the system can keep the temperature controlled. The TR21-A, based on the IEC60751, has a T50 with less than 4.7 seconds and a T90 with less than 12.15 seconds.

Also, you’ll need a good process connection, but WIKA, as always, is on that. You’ll find an extensive list of process connections, so I’m sure one will fit your process requirements.

Lastly, you can calibrate the device without opening the process. Of course, I kinda take that point for granted. Its small size means you can fit it just about anywhere, and that’s it! No fancy features here.


On the upside, the WIKA TR21 offers a wide measuring range and good process connections. On the downside, it lacks an open protocol like HART, and the configuration even with the free software doesn’t provide the best user experience.  In general, this thermometer could save you a few dollars if you have a tight budget, but scale it and price it before you buy it.

I didn’t find a TR21 video, so have a Haikaiss video instead:

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