Analog loops (4-20 mA) are used worldwide, and HART communicators also operate over 4-20 mA loops. The HART communication protocol makes it possible to transmit digital and analog communication over the same channels, for example, between sensors and a control system.
To know more about HART, you can read the Visaya Article on HART Communication Protocol
Advantages of the HART communication protocol
HART communicators and HART modems are designed to communicate with field devices using the HART communication protocol. They are instrumental (pardon the pun) to the work of field engineers. These devices make our lives easier when we have to commission a field device or check the status remotely. Not having to climb a tank to configure a level radar is quite an improvement in the life of the field engineer.
What is a HART communicator?
A HART handheld communicator is a remote device that gives access to a field device’s menu, allowing the engineer to change the setup and check data from the device. Sometimes we can also save the configuration and download it to a similar device but not all brands have this feature yet.
Earlier HART handheld communicators (also known as handhelds) could only communicate with devices that use the HART communication protocol. Today, vendors offer compatibility with the most common communication protocols: HART, FOUNDATION Fieldbus, and even PROFIBUS PA, although the latter option is less common.
To know more about Wireless HART configuration, you can read the Visaya Article on WirelessHART Configuration
The Best HART Communicator
The Endress+Hauser SMT70 is probably the best HART Communicator in the market today. This is essentially a tablet PC that comes with pre-installed driver libraries. Its touch screen is easy to use and is a complete solution to manage field instruments throughout the entire life cycle. It also functions as a Windows tablet to check emails, navigate search, install other software, connect to Wifi, make calls, etc.
Furthermore, this tablet has all the approvals and certifications necessary to work in harsh environments. New devices can have Bluetooth or even a web server, so we can configure the device without any particular software or tool, just with the browser (IE, Chrome, Edge, Firefox, and so on).
How does a HART communicator work?
HART handheld communicators work using software that interprets a device description (DD) to properly display the data from that device. HART communicators 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 we can add more if necessary too. To receive the information, we have to connect the handheld communicator to the device using a 250-ohm resistor.
Why do HART communicators need 250-ohm resistors?
If you are a field engineer, you never know when you will need a 250-ohm resistor. So you probably carry one around in your pocket.
The HART communicator uses an analog-plus-digital protocol. HART understands 1200 hertz as “1” and 2200 as “0.” For the HART communicator to read data, we need to create an impedance on the loop. In most applications, we already have one, but sometimes we need to create a minimum of 230 ohms, according to the recommendation of FieldComm Group.
If we don’t have the impedance already in the control system, we’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 vs series connection
This one comes up a lot, usually with four-wire field devices. This is because the concept of passive and active output can create confusion.
We can connect the communicator in two different ways:
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.
Connect the communicator using the comm port of the field device. Most field devices have a comm port, so usually, series connections are the easier way.
If you don’t have the impedance, just use the resistor you carry in your pocket (you always should) to establish a communication between the device and the communicator.
And now, four-wire devices. First, we need to connect the resistor from the 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.
What is a HART Modem?
A HART modem is a device that converts a PC or mobile device into a full-featured HART communicator. The USB or Bluetooth connection makes it possible to have bi-directional communication between a Smartphone or a PC/Laptop. Then the device receives the digital communication transmitted in the analog loop.
A HART modem is a cheaper option than a HART Handheld communicator. But only if you already have a laptop or tablet that has enough battery life to withstand factory conditions.
The best HART modems
We would recommend using HART modems like the ProComSol HM-USB-ISO or the Commubox FXA195 by Endress+Hauser. These devices have more or less the same features but the Procomsol model is a cost-effective solution, and also a part of the FieldCom Group. Here, we build the connection in a similar way as we explained earlier with the handheld communicator.
Device descriptions (DD) for the HART communicator
The HART communicator needs to understand as well as display data from the field device in a user-friendly interface. The information doesn’t pop up on the screen like magic; to make this happen, we need files to help the communicator understand the information and organize it. These files are called device descriptions or DDs. Most handhelds have entire libraries with thousands of DDs already installed.
However, sooner or later, we will have to upgrade these libraries for new devices or revisions. If we don’t have the proper DD file, we’ll only get a generic view of the device and can’t change most of the information.
This particular procedure can vary among HART handheld communicators. Usually, they have similar requirements, but we need to ask the vendor to make sure about it.
Most of the time, we need a license to upgrade the DD library. When we buy a new HART communicator, we get a 3- or 5-year license to upgrade the library at no cost. Once this license expires, we have to buy a new one. We can find exceptions to this rule but this is pretty common. Furthermore, we’ll probably need to convert the files before we install them. Sometimes, the procedure to convert is simple, but there might be times where it is needed to delete the files.
The Perfect Software for operating HART Field Devices
There are several software options to set up field devices for free, for example, Pactware and DeviceCare (only Endress+Hauser devices). But we will need to download the library or DD/DTMs from the vendor´s page manually.
In case we want software with the complete library of Field HART devices in the market, the best software depends on the usability that we want to have. For point to point connections, the best option is the DevCom2000 Smart Device Communicator. From the first minute of installing this software, our laptop will be able to scan the network through the HART modem and connect to any HART field Devices to configure it!
In a scenario where we are supposed to create projects and networks, we need to monitor and configure all the field devices installed in our plant. Here, one of the interesting options is to combine Pactware and the Codewrights library. This is certainly one of the best options when it comes to price and quality.
On the other hand, if you want a complete software with one of the best interfaces and usability, Fieldcare by Endress+Hauser is the best choice. Though a pinch on your pocket, it has very high standards of quality.
Some customers consider configuration an essential feature in a HART communicator. With this, not only we are able to configure the field device, but also make replicas with the same configuration. The first step is to download configurations from the field device and upload them to a different device. This can shorten the setup time of a new device to a few seconds.
Most HART communicators will allow us to upload a configuration to a new device easily if the device is of the same type. However, some communicators, depending on the software, will let us download the configuration but only for comparison purposes (pdf document), rather than for uploading. This means that if we want that configuration, we have to do it manually.
To know more about the HART communicators, you can get in touch with our engineers!