Thermistors Vs RTD

Thermistors Vs RTD – What Are the Differences?

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As you’ve clicked here, we’re assuming that you already know what Thermistors and RTDs are made to do. But there’s confusion pops out while choosing a side when it comes to thermistors vs RTD as they both are made to measure temperatures.

Now the question is, which one is better for you to pick? Well, for reaching any decision when there’s more than one option, we always focus on the differences. You need to do the same here if you want to end up with the right choice that can get you a better result.

So, what makes them different from each other? Let’s put some light on that.

What Are RTD and Thermistors?

We don’t know how much you actually know about these two, but if you’re not much enriched on that side, we owe you the definitions of both. So, what actually are RTD and thermistors?

RTD

Resistance Temperature Detector, or what we mostly know as RTD is a resistor that is used to measure temperature. Its working principle is, there will be changes in resistance if there are any changes taking place in the temperature.

Basically, the conductor’s resistance is responsive to the change of the temperature, and this is what helps RTD in measuring temperature. RTDs are mainly a structure formed from pure metal, and the list includes nickel, platinum, copper, etc. On top of that, a ceramic substrate protects it.

The major function of platinum is to help the RTD withstanding high temperatures. Another added advantage of this material is it’s highly stable. Thanks to the metals for their high-temperature coefficient as that’s what leads to an increase in their temperature once the overall temperature starts rising.

Thermistors

Clearly, this thermal resistor is also made to measure temperature. They’re basically a construction of composite materials, which are in most cases metal oxides like manganese, copper, or nickel. And yes, there are stabilizers and binding agents as well.

Due to being a semiconductor material structure, it comes with both negative and positive temperature coefficients. The positive one means the increase in temperature leads to an increase in resistance.

On the other hand, in the negative one, it’s inversely proportional. Yes, we’re talking about the temperature of the resistance.

The reason for the growing popularity of thermistors is mainly backed by improvements in controllers and meters. Thanks to the sufficient flexibility of meters lately, that has been playing an amazing role in broadening the range of thermistors set up and also eased up interchanging the probes.

Thermistors vs. RTD: the Differences

Whenever you make the right decision about anything, it mostly comes out as a result of choosing the right option. But it works only when you know what has made the best option better than the others. Well, that’s quite the same thing when you’ll have to choose one from the thermistor and RTD.

Though they’re made to do kind of the same job, which is measuring temperature, there are certain aspects that have made them different from each other such as:

Range

When the temperature range is small, it’s better to go with the thermistor. After all, it’s capable of measuring up to 130°C easily. But when you’ve got some bigger numbers to cover, the RTDs are considered a better option.

Actually, certain kinds of RTDs can go up to a number like 600°C. So, if the application you’re planning to give a shot involves any temperature more than 130°C, you don’t need to think twice before picking the RTD probe.

Sensitivity

If there are any changes in temperature, both RTDs and thermistors respond to a predictable change in resistance. But the difference is when it comes to change resistance, thermistors are ahead of RTDs as the rate here is 10 ohms/degree, which is indeed higher than RTDs.

And don’t underestimate the thermistor’s sensing area just because it’s small. Even with that, its response time thermistor is better than the RTD as it can detect temperature faster. So, clearly, thermistors are more sensitive than RTD.

Accuracy

When you look at the finest RTDs, their accuracies won’t be much different than thermistors. But they surely can add resistance to your system. Now, the problem is when you’ll use long cables there, the alteration in reading might go beyond acceptable error levels.

But with a larger thermistor, the sensor’s resistance value goes higher with the size. So, when it’s long-distance, and you’ve got no way to add any transmitter, the thermistor can surely nail the job.

Characteristics Graph

Like a ton of other things, these two are different from each other on the basis of the characteristic graph as well. Yes, we’re talking about the one between temperature and resistance. For RTDs, it’s linear but for thermistors it’s nonlinear.

Size, Hysteresis Effect, and Resistivity

We don’t know what you think about this aspect, but if you want to know about the size, RTD is comparatively larger than the thermistor. But in the race of resistivity, the thermistor is on the higher side. And the hysteresis effect? Well, once again, it’s high on the thermistor.

Application

So, where are you thinking about using these? Is it for home appliances or industrial? If it’s the first one, then the thermistor is going to be just perfect as it’s good with measuring smaller temperatures. But when you’re planning to move to the second one or the industrial, we say you go with the RTD.

Cost

We all need to look at our pockets at times, and we guess you do too. So, when you’re thinking about the cost of these two, you can get thermistors without spending too much from your wallet.

But if you’re not afraid of pushing the expenses a little higher for better performance, then you’re always welcome to try the RTDs.

Before you go for thermistors, as they’re cheaper, let us tell you the thermistors that have extended temperature ranges are going to cost even more than RTDs. The same goes for the one with interchangeability features as well.

Comparison Table

We won’t be surprised if you’re still not being able to decide which one is going to be better for you. Don’t worry; we think we’ve got an idea to ease that up. Yes, we’re talking about a comparison table, and here it is –

Base of Difference Thermistor RTD
Accuracy 0.05 to 1.5°C 0.1 to 1°C
Long-term stability @100°C 0.2°C/year 0.05°C/year
Temperature Range -100 to 325°C -200 to 650°C
Linearity Exponential Fairly linear
Response time 0.12 to 10s (Fast) 1 to 50s (Slow)
Sensitivity High Low
Hysteresis Effect High Low
Resistivity Low High
Size Small Large
Cost Low High

Final Words

Obviously, you can’t choose both when it’s all about thermistors vs RTD. This clearly indicates that you need to go for a deeper comparison in order to figure out the right one for you. So far, all we’ve tried to do is get you that. Now you decide which one you really want on your shopping cart this time.

Related Posts:

Thermistors vs. Thermocouples: What’s the Difference?

What Are the Uses of Thermistors?

What Is a High Precision Thermistor?

Resources:

1. https://en.wikipedia.org/wiki/Resistance_thermometer

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