Your HART communicator and you
If you work in instrumentation, then the HART communicator is a part of your body in the field! But sometimes you can’t get it to work properly, or maybe you don’t know how to use a particular function, right? Don’t worry; in this article, I’ll cover the most common issues people have with HART communicators and try to help solve the problems or avoid them.
Why am I saying “HART communicator” rather than “handheld” or another name? Yes, we have several names for this style of device. However, in this post I want to specifically address issues with HART devices.
Most of these problems come from a lack of core knowledge. I’ve spent a lot of time updating and repairing HART communicators and training end users on proper use. This experience helps me understand these issues better than the average user. One of the most important lessons I learned is that the perfect HART communicator doesn’t exist. If you don’t have to pay to upgrade the database, then you have to depend on the vendors for updates and so on. It’s all give and take.
You’ll need some basic knowledge to understand all the following points. If you lack the basics or just want a refresher, then you can check out this post. You may also have questions related to handhelds in general. We answered many of those a while back, so check here for our list of questions and answers.
Okay, now let’s work on the six most common issues with HART communicators!
You never know if you need your 250-ohm resistor or not, am I right? In fact, you always carry the resistor with you for that reason. But do you know why do you need a resistor in the first place?
The HART communicator uses an analog-plus-digital protocol. HART understand 1200 hertz as “1” and 2200 as “0.” For the HART communicator to read data, you need to create an impedance on the loop. In most applications, you already have one, but sometimes you need to create a minimum of 230 ohms, according to the recommendation of FieldComm Group.
If you don’t have the impedance already in the control system, you’ll need a 250-ohm resistor to create that impedance and communicate with the field device. That’s it. Easy, huh? On to the next one!
Parallel or series
Yep, this one comes up a lot, usually with four-wire field devices because the concept of passive and active output can create confusion.
Let’s start with the idea that you have an impedance already on the system. You can connect the communicator in two different ways.
Way One – connect the HART communicator parallel to the device’s output, with one device cable on the positive side and one on the negative side. This basic connection, with the impedance, will communicate without issues.
Way Two – connect the communicator using the comm port of the field device. Most field devices have a comm port, so usually this is the easier way.
When you don’t have the impedance, just use the resistor in your pocket to establish communication between the device and the communicator. That’s why you always carry it, right?
And now, four-wire devices. First, you need to connect the resistor from positive to negative output. Then connect the HART communicator parallel to the resistor to establish the communication. Take a look at this graphic if you need help visualizing the connection.
Device descriptions (DD)
The HART communicator needs to understand the data coming from the field device. The information doesn’t pop up on the screen like magic; you need files to help the communicator understand the information and organize it for you. We call these files device descriptions or DDs. Most handhelds have entire libraries with thousands of DDs already installed.
However, sooner or later you need to upgrade these libraries for new devices or revisions. If you don’t have the proper file, you’ll only get a generic view of your device and can’t change most of the information. I meet engineers who say that they need new or different communicators just because theirs don’t show all the information coming from the field devices. Now you know why; you don’t need to change your field device. You just need to install a new DD. But that brings us to another issue.
This particular procedure can vary among HART communicators. Usually, they have similar requirements, but you should ask your vendor to make sure.
To upgrade your DD’s library, most of the time you need a license. When you buy a new HART communicator, you get a 3- or 5-year license to upgrade the library at no cost. But once the license expires, you have to buy a new one. You can find exceptions to this rule, but it’s pretty common in the market.
Furthermore, you’ll probably need to convert the files before you install them. Sometimes, the procedure to convert is simple, but I’ve lived situations where I had to delete files and things like that. You may want to consider getting an expert to help for those.
Updates and conversions vary by vendor, so again, you should find out what you need to do and when before jumping in.
Some customers consider this feature a requirement from a HART communicator. Downloading configurations from your field device should give you little trouble. Uploading the same configuration for a different device, on the other hand, can run into a wall.
Most HART communicators will allow you to upload a configuration to a new device easily if the device is the same type. However, some communicators will let you download the configuration only for comparison purposes rather than for uploading. If you want that configuration, you have to do it manually.
The most common problem! You can’t find anything wrong, and you have the resistor and all the DDs you need, but you get bupkis when you try to communicate. You’re stumped. My advice? Check how your HART communicator scans the field device.
Usually, you just connect the communicator and the magic happens, right? Well, most communicators default to searching for the device with zero as the polling address. However, some devices have different polling addresses. If your communicator only searches for zero, then you won’t find the device.
For examples, wirelessHART adapters come with high polling addresses, the THUM from Emerson has the polling address 63, and the Adapter from Endress+Hauser has the address 15. Check the polling address of your device, then set your communicator to look for that address. Or you could change the communicator configuration to search a range of polling addresses. Either way should get you there.
That covers the six most common issues users have with HART communicators. If you have questions, share them in the comments, and we’ll answer them!