TBM | Bi-Metal Thermometers
Winters TBM Bi-Metal Thermometer
TBM is used in industrial process, heating and air conditioning, ventilation and wastewater applications.
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Now we’re going to talk about Winters TBM series, which is the bi-metal thermometer. This thermometer is the most common used in, mainly, the industrial application. Bi-metal thermometers generally come in 304 stainless steel cases.
Let’s talk about how a bi-metal thermometer works and how they're set up. Bi-metal thermometers come in three configurations. You’ll notice we have here, this is called a back connect and that certainly looks kind of like your meat thermometer you might see at home, with the stem coming straight out the back. This is a bottom connection; it comes out and then, of course, does a right angle. Then one of the more common is an adjustable angle where it can be adjusted at a 90 degree angle, it can be either straight out the back or anywhere in between so that, if it’s up on a pipe or something, they can bend it down so it can be seen. The two most common configurations are the straight back connect and the adjustable angle.
The most common sizes here used in the US marketplace are the 3-inch dial size and the 5-inch. They are also available an inch and a half or a 1 inch, which would be a pocket-size, a 2-inch for laboratory, 4-inch, and 6-inch, which tend to be more on the European specs.
The ranges that you can achieve with a bi-metal thermometer are -40 degrees is our lowest range up to 1000-degree. As you can see here, this one is a dual scale, and it’ll be Fahrenheit and Celsius, and it can also come as this one, as a single scale. You’ll notice it has what we call a dish dial. The reason it’s a dish dial because it allows you to be able to determine better what line of the increment of the scale that the pointer is pointing to. That dish dial is referred to as an anti-parallax dial, which means you won’t see it wrong if you’re looking at an angle.
A couple of other things about bi-metal in general are this: We do stem lengths from 2 ½ inches. We can go all the way up to 110 inches, but the most common stem lengths are 2 ½, 4, 6, 9, and 12. Those are the things you would normally find in stock. Again, with a variety of different temperature ranges.
You might say, “How do I know what stem size I have?” Whenever you measure a stem on a bi-metal thermometer, make sure you include the threads. This is a 2 ½ inch stem, but if you measured from just below the thread to the tip of the stem, you might tell the person you’re trying to order it from, “It’s an inch and a half.” Please, make sure you include that.
Another feature of all our bi-metal thermometers, if you’ll notice, there is a screw on the back with a slide. What that allows you to do, by turning that screw, it would rotate the dial. So if you had a calibration issue and it was off a little bit and you had a known standard, you could tweak the calibration by rotating the dial slightly.
One of the most important things with a bi-metal thermometer is to make sure you have full immersion of the stem into the process that you’re trying to check the temperature on. This has a bi-metal element in it which is approximately an inch and a quarter long, so for this to read properly, you need to be inserted into the process at least an inch and a quarter. If you were only a half inch into the process, then you would get some errors in your reading.
One of the things you want to do with a bi-metal thermometer is you always want to use a thermowell when you can. What’s a thermowell? Here’s a thermowell and what it does is the bi-metal screws right into it. In this case, this happens to be a 316 stainless steel well, but the thermowells also come in 304 stainless and brass plus other exotic materials, if you have high corrosive process. The importance of the thermowell is this: With the thermowell, if you insert it into a pipe or a tank and a bi-metal needed to be replaced, you could just unscrew the bi-metal, take it out, and get a new one and put it in. If you did not have the thermowell, you’d have to drain the tank, you’d have to empty the pipe, otherwise, the process would come out when you took the bi-metal out. Whenever you’re doing applications, always look to use a thermowell. Again, we have thermowell sizes to fit every stem length that we make.
The other thing about bi-metal thermometers, they come standard with a glass lens. They are hermetically sealed. The reason is, if they’re used near heat and steam, if it wasn’t sealed, the inside of the lens would, again, become cloudy and once that becomes cloudy, you can’t read the dial. That’s why they have the hermetically sealing.
All manufacturers of bi-metal thermometers, standard, use the half inch MPT and they use the same stem length configurations. That way, if you’re replacing someone else’s with a Winters, as long as you know it’s half inch with a certain stem, our thermometer will fit into the same thermowell.
The diameter of the stem, as a standard, is quarter inch. That’s why the bore size on these thermowells are .260. The option is you can get this stem with 3/8, so .375 is also available. Again, this is 304, you could get this part of the bi-metal with 316 stainless steel as an option, and some people do that because they’re using it in a process that is corrosive and wouldn’t work with the 304. But if you’re using a thermowell, then the 304 should be fine.
Bi-metal thermometers can be used almost anywhere. The advantage of a bi-metal is that if you have a close pipe, you can use your short stem and still fit it in. If you have a tank, where you want to get halfway down the tank, you might have a 30-inch stem on the bi-metal thermometer. That’s the flexibility that a bi-metal gives you, that it can be used, as a matter of fact, we do sell quite a few to brew guys that use them on their home brewing equipment and they have to have a bi-metal so they can get the temperature of the mash. They can be used on air, they can be used anywhere where you want to sense temperature.
We did talk about that, we said the case material is 304 stainless steel. As we said, we have the three, bottom connect, back connect, and in this case, adjustable angle. The two most common dial sizes are 5 inch and 3 inch, and then again, others are available upon application. Accuracy of a bi-metal thermometer is 1% full-scale.
Again, the biggest thing is to make sure you’ve got full insertion of the sensing element, which is going to be at least the last inch and a quarter to inch and a half of the stem. We always recommend you use a thermowell because it’s just going to protect your unit and allow you to change it without having to shut everything down.
Thermowells do not come standard with bi-metals, and there’s several reasons for that. We never know what the material is that may be needed by the customer. It could be as easy as brass because it’s being used in chilled water or whatever, but it may also be an acid-base or a corrosive. Sometimes a thermowell even needs to be made out of an exotic alloy like Hastelloy.