USB in the Field
| 10/10/2016 2:14:41 PM
USB was intended to simplify and standardize the connection of computer peripherals. It has proven to be a great improvement over RS-232. Connectors have been standardized, devices are hot swappable, and many can even be powered by the host USB bus. But the devil is in the details. USB was designed for the office, not for troubleshooting equipment out in the field.
Granted, you won’t be using USB as your controls network. But you may very well need to collect a bit of data, update a program, or troubleshoot a system using your laptop computer. It’s unlikely that your laptop would have a serial port these days, and many of the field devices will lack a USB port. If you want to connect, you’re going to need a USB-to-Serial Converter.
I strongly recommend using a converter with isolation. Even though USB cables use twisted pair wire and shielding, the USB specification wasn’t designed for industrial environments. Electromagnetic Interference (EMI) can still interrupt data, causing your port to disconnect. Worse yet, ground loops -- currents caused by different ground potentials between your computer and the device that you are talking to -- can actually destroy your PC. An isolated converter protects you from EMI and ground loops. It provides a physical barrier between your computer and the downstream device.
When you are troubleshooting in the field you will want to know if data is actually flowing. I may be stating the obvious, but if your converter has LEDs it eliminates a lot of the guesswork.
You will also want solid USB connections. Standard USB ports are designed for office use. They don’t grip the cables firmly enough to stand up to the conditions you’ll encounter in the field, like heavy vibration or the simple fact that you’re more likely to yank things loose when the USB cables aren’t conveniently hidden behind a desk. Your converter should have high retention USB ports.
If you’re dealing with RS-422 and RS-485 connections, pluggable terminal blocks come in handy, too. They allow you to take the terminal block off the converter, which makes wiring much easier. When you’re finished, you just plug the terminal block back in and you’re ready to go.
So these are the features that I recommend looking for when buying a USB-to-Serial Converter for portable use in the field:
- High Retention USB Ports
- Data Indictors (LEDs)
- Pluggable terminal blocks
Our USOPTL4 includes all of these features. Check it out here:
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