The Universal Serial Bus (USB)
Dew Point
October 8, 2022Understanding Accuracy Specifications
October 8, 2022
Industrial instrumentation often connects to a PC, and more often than not this is by USB.
I think most of us have cursed when the USB hasn’t performed as we want or expect it to do, but it remains an elegant system, and its abundance in the consumer environment, makes it a subject worth re-visiting.
We thought an overview of the system might be useful.
USB has standards; from USB 1.0 to USB 3.1 at the time of writing. These talk about the speed of data transfer predominantly. The following (simplified) table summarises this:
It’s worth noting however that the type of connector doesn’t necessarily tell you what the standard is. For example, the USB “C-type” connector may be an implementation of USB 3.0, USB 3.1 or even Thunderbolt 3, whereas USB 1, 2 and 3 can all look the same with very different performance. (Most commonly the plastic guide on a USB 3 is blue)
Recently the Homershams office bought a few new PC’s. We went with the Intel NUCs as they are small and powerful. But on the rear, we see a special case example of the USB-C being a Thunderbolt 3.
Thunderbolt 3 carries not only USB 3.1 data, and hence has huge data transfer speed (up to 40,000 MB/s) but also carries PCI-express data, DisplayPort data and up to 100-watts of DC power which can power a laptop directly!
Charging & Power Supply
As mentioned above, USB provides both data transfer and power supply for peripherals. The original USB specification called for 5-volts at 500mA, but later iterations have added fast-charging and higher current delivery.
In the example below, we see an application of “Adaptive Fast Charging” for a cell phone. In this case the Quick-Charge 2 specification allows 9-volts (instead of the standard 5-volts) on compatible phones.
Handheld Instrumentation RS232 to USB
It used to be standard to have a RS-232 output on instrumentation, which is then converted to USB via a “UART” converter. An example being our Center 309 4-channel loggers and Additel Process Calibrators.
This can cause Windows to be confused about assigning COM-ports. If you run into a problem with an external RS232 to USB, check the device manager for the COM port assignation.
The latest instruments from Center (e.g. C520) have micro USB out and plug directly to USB so this doesn’t occur.
