Q&A: Temperature transmitters enhance accuracy, safety and cost effectiveness

Greg Pryor is the Temperature Product Marketing Manager at Endress+Hauser USA. To help answer some questions surrounding temperature transmitters, we sat down with him to learn more about temperature transmitter safety, usability and more.

Could you give us a brief overview and history of temperature transmitters and their impact on various industries?  

To understand transmitters, you must remember that their base function is to take the input from either an RTD or a thermocouple and convert that into a 4-to-20 mA output. When a thermocouple gives out its production in millivolts, it loses its signal strength over distance, and both RTDs and thermocouples need an IO card somewhere down the line that will take either an RTD or a thermocouple-specific input. At some point, the thought behind transmitters was to take and convert those outputs into a 4-to 20-mA analog output to standardize that signal output while simultaneously boosting the signal via power from the transmitter. It can send 4-to-20 mA longer distances. You can also use that same wiring with a suitable transmitter to transmit additional data on top of it if you have, for example, HART protocol. On that two-wire instrument cable, it receives not just a millivolt output from a thermocouple; it’s converting to a 4-to-20 mA, so you’re getting your temperature, but you can also get other pieces of information via HART protocol.  

It’s important to remember that not all transmitters have HART. That was added after the fact. At their core, transmitters were first designed to convert and send a 4-to-20 million mA output. Then, various additional communication protocols were added later, then things moved to digital, like PROFIUBUS or Foundation Fieldbus, and now things are moving towards Ethernet-APL. At Endress+Hauser, our transmitters have evolved with communication technologies, and we’ve continued adding additional functionalities to them to stay optimal.  

Safety is essential in terms of instrumentation. But regarding temperature transmitters, why must consumers strongly focus on safety?

If you consider temperature a measured value in industrial settings, you have many processes that need to be controlled by temperature. However, it depends on the industry and the application. But let’s take milk, for example. To pasteurize milk, you must bring it to a specific temperature and hold it there for a certain amount of time, which will eliminate bacteria. If you’re not measuring that temperature accurately, there could be issues and challenges. What if you didn’t bring the temperature up to pasteurization levels? Now, you have a batch of milk that didn’t get pasteurized—a recipe for disaster. Let’s say you have a chemical application that requires some reaction. That reaction may occur at a specific temperature or in a particular temperature window. If you’re not accurately monitoring those temperatures, you can’t maximize the efficiency of that reaction. And then, we could discuss grain storage in a silo. When bacteria start growing there, it generates heat that can be recognized before total spoilage happens to the batch—another recipe for disaster. So, temperature measurement is essential.  

Similarly, usability is critical. What are the main factors in determining a temperature transmitter’s usability?  

Suppose you think back to what I was saying earlier about how temperature transmitters can take input from an element and emit a 4-to-20 mA. They can all do that if that’s all you need it to be able to do. Then, you don’t need any additional functionality. You start to get differentiation through the transmitter portfolio when you need a dual input or a dual channel transmitter, where you can take two temperature elements into a single transmitter. That gives you additional functionality like sensor backup, averaging or drift detection. Those other functions can only happen if you have a dual-channel transmitter. But only some processes are going to require that.  

If you’re trying to decide on a transmitter, you must determine the level of complexity you need. If you need a 4-to-20 output, you can purchase a basic transmitter that converts to 4 to 20. If you’re using HART protocol, step up to one with HART. Bluetooth functionality is another feature you can look for. Endress+Hauser has transmitters with the option to configure them via Bluetooth. You can use the app on your phone or tablet, so you don’t have to physically connect something to the device to reparametrize or program it.  

What factors should a customer look for when scouting reliable and cost-effective products? 

Regarding cost-effectiveness and temperature transmitters today, they are different from years ago. If you’re working on a budget, there are different price and functionality ranges for these devices, so if you need them, you should be able to purchase them.  

How accurate are modern temperature transmitters?   

It depends on the transmitter, but they have continued to improve their accuracy. Every RTD has variations when they are built, so a curve indicates the specific number of ohms that equates to a particular temperature. Calibrating that RTD and getting the Callendar-Van Dusen coefficients is unique to that specific RTD. With sensor transmitter matching, you can then program those into the transmitter. The transmitter is set for the ideal RTD right with zero error. If you then program those constants into the transmitter, the transmitter will linearize the curve to the actual RTD, so it can eliminate your measurement error from the RTD, which tightens up your accuracy and improves safety.  

Regarding temperature transmitters, what should people look for when working with or purchasing from a company?

Because there are so many different transmitters and ways to set them up, having a vendor to help you configure your instrument is essential. Having someone you can contact if you have an issue or questions post-sale is important. A best practice would be to ensure the manufacturer has technical support because transmitters can—at times—be complicated instruments. There are some nuances that maybe you’re not as familiar with, but having somebody you can pick up the phone and call or send an email and promptly get a response with their technical support on the back end is beneficial. It’s pivotal to have a company by your side pre-sale and post-sale. I would look for holistic, safe, reliable, accurate products and customer support when scouting partners for your process instrumentation needs. 

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