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? This is why we put together this guide for you.
Why are we saying HART communicator specifically rather than handheld communicator or another? Because the HART communicator is one of the most popular devices of its kind, and in this article, we address issues particular to it.
What is a HART communicator?
A HART communicator gives you access to a field device’s menu, allowing you to change the setup and check the data from the device. You can sometimes save the configuration and download it to a similar device as well. Not all brands have this feature, though.
To know more about this HART communicator, you can check out the Visaya Product Review
How does a HART communicator work?
Once upon a time, HART communicator (also known as handhelds) could only communicate with HART devices. Today, we have vendors offeringHART, FOUNDATION Fieldbus, and even PROFIBUS PA, although that last option isn’t common.
In general, the HART communicator gives you access to a field device’s menu, allowing you to change the setup and check the data from the device. You can sometimes save the configuration and download it to a similar device as well. Not all brands have this feature, though.
As for how it works, it has software that interprets a device description (DD) to properly show the data from that device. HART communicator come with a standard database that includes a wide range of vendors, devices, and versions. A new handheld can have more than 2000 DDs pre-installed, and you can add more if necessary.
You establish a connection with the field device using a 250-ohm resistor. This schematic shows how to connect a handheld to a HART device.
In short, this service tool lets you connect to HART field devices and set them up, check their diagnostics, and read their data.
The Perfect HART Communicator
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.
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 handheld communicators in general. We answered many of those a while back, so check here for our list of questions and answers.
To know more about Handheld Communicators, you can read the Visaya Article here
You can find a field communicator with the best features for you. In the article here, we review some features that might support you with your requirements.
If you want to get a new handheld, you have options that can power your device so you can skip the external power supply. That’ll make your life easier. Certain HART and FOUNDATION Fieldbus devices have this feature, and some can also power up PROFIBUS PA devices.
You can check out SMT70 in our shop. This is a tablet PC designed as a complete solution that comes with pre-installed driver libraries. It is an easy-to-use, touch-enabled tool, which can be used to manage field instruments during their entire life cycle.
Furthermore, we assume your field communicator uses only HART. You can choose tablets with more than HART communication. These tablets have all the approvals and certifications necessary to work in harsh environments. And new devices can have Bluetooth or even a web server, so you can configure your device without any particular software or tool.
250-ohm resistors in 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.
To know more about control systems, you can read the Visaya Article here
Parallel or series connection
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.
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) for the HART communicator
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.
HART communicator configurations
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, wireless HART 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 the HART communicator. If you have questions, share them in the comments, and we’ll answer them!
To know more about the HART communicator, you can get in touch with our engineers!