How to Address Common USB to RS-232 Adapter Cable Issues

Have you had trouble connecting your RS-232 device to a computer with a USB to the RS-232 adapter? If so, you’re not on your own. Many of our customers have problems with these adapters. In this article, I’ll briefly discuss where these problems come from and give you some ideas for how to deal with them.

The Importance of An Adapter
Since USB has become so popular, most computers sold today do not have an RS-232 port. So, to connect an RS-232 device like a CR1000 to a laptop, you need a USB to RS-232 adapter like the 17394 converters.

USB to RS-232 adapters do something important but also have some problems. For example, when you use a USB to RS-232 adapter, you might run into three kinds of issues:

Driver problems

Hardware problems

Performance problems

Issue 1: Driver
Our customers’ most common problem with a USB to RS-232 adapter is installing the right driver. The driver must match the chip inside the cable, not the cable maker.

Two major companies make chips from USB to RS-232: Prolific and FTDI. Campbell Scientific recommends and sells a cable with an FTDI chip because off-brand chips with bad drivers are unreliable (part number 17394). We chose this cable because it has a chip for which Windows Update has a certified driver. (The older cables were silver, and Windows versions above 7 didn’t have a driver for them.)

If your adapter’s driver doesn’t get installed automatically or can’t be installed from a CD, you will need to find the driver for your cable’s chip on the Internet. Some companies write on their packaging which chip is inside their cable. Follow these steps in the Windows Device Manager to find out what chip is in a cable:

1. Right-click your device from the list in the Windows Device Manager.

2. In the resulting drop-down menu, select Properties.

3. Select the Details tab within the Properties dialogue box.

4. Select Hardware Ids from the Property field’s drop-down menu.

5. The Value field contains both a VID (Vendor ID) and a PID (Product ID) (Product ID). These IDs indicate the chip’s manufacturer and model number, respectively.

6. Once you know the type and manufacturer of your chip, you can locate and download the correct driver for your Windows version.

Issue 2: Hardware
USB to RS-232 adapters are standard components of computer hardware. As much as we’d like everything to be as dependable as the CR1000, all adapter cables eventually fail.

Although there are two primary manufacturers of USB to RS-232 adapter chips, there are numerous cable manufacturers with varying quality cables.

Higher-quality industrial models should last longer, but like any other field tool, they wear out over time.

A badly made cable could have parts that break in a short amount of time, even before you get the cable.

Issue 3: Performance
As we’ve already said, USB uses a shared data bus and packetized communication. With packetized communication, some latency (the time it took for data to be sent) wasn’t there with RS-232 ports. Unfortunately, when you download a lot of data or a new operating system, latency makes a difference that you can see.

With the driver for FTDI chips, you can reduce the time between packets. To do this, you can use the Windows Device Manager to get to the Latency Timer field. Do these things:

Right-click your device on the list in the Windows Device Manager.

Select Properties from the drop-down menu that appears.
Click the tab called Port Settings.

Click the button “Advanced…”

For the best performance, go to the Advanced Settings window, find the Latency Timer field, and change the setting to 1.

The Bottom Line
The CR6 is a newer data logger with a built-in USB connection. Still, many devices will have RS-232 links for years, so we’ll still need to use adapter cables that go from USB to RS-232.