Introduction
The U1282A multimeter supports a high speed logging capability which I was keen to test.
By high speed it means approximately 10Hz indefinitely (my test was for 8 hours using the supplied software, I have not tested this software for a longer period yet). The 10Hz rate looks to be a sweet spot, fast enough to be useful for many scenarios, with the extreme accuracy of a multimeter. It makes an incredible data logger. The only limitation would be that one multimeter is never enough. The data logger capability is built-in to the multimeter (it has built-in memory for up to 10,000 data points) but it is also exposed through the Infra-Red to USB (IR-USB) connector that can attach to PCs and can be used with Keysight's free Handheld Meter Logger Software for hundreds of thousands (tested) data points at a minimum. There is no practical limit if there is sufficient memory and disk space until the battery on the multimeter expires. The logging capability would be excellent for observing circuit and device behaviour over long periods for the purposes of temperature testing or current consumption measurements for instance.
The Keysight PC application data logging feature is described in this blog post.
How does it work?
The multimeter looks like a COM port to the PC and as a SCPI device to the software through VISA drivers. In brief, once the IR-USB connector has been clipped on the multimeter can be controlled and monitored via the PC just like any other test instrument.
It is possible to connect using 9600 baud and send SCPI format messages using custom software too. The Keysight software presents the collected data in the form of graphs and tables, and it can be exported to Excel or other software.
The Handheld Meter Logger Software was downloaded from the Keysight website and it was straightforward to use. The left side area is used to configure up when to capture data. The remainder of the area can show graphs, a huge live display of the multimeter LCD or show tables of data. If you have multiple multimeters then they can all share the same software; the display can be split horizontally, vertically or into grid tiles for up to 9 multimeters.
The graphing functionality is no replacement for a true math program but it does allow you to insert time cursors and examine the min, max and average over the period. The data can be exported to Excel (not advisable with massive data sets) or MATLAB or your choice of software; it can be exported in CSV format.
The software looks a bit version 1.1 (but it is version 3.1!) in that although the functionality described works and nothing fatal was experienced, some things could be further improved for a bit more usability or without workarounds. There are nevertheless some very interesting capabilities which I briefly tried.
Data Logging with a Remote Switch Probe
One feature that I am going to be using a lot of is the ability to log individual readings with a press of a button on a probe. This is exceedingly powerful. One use could be to measure voltages on multiple test points on a board. It would be possible to rapidly collect all measurements together. An audible beep tells you that the measurement has been collected. Data points can be deleted if needed.
The Remote Switch Probe (U5404A) is essentially just a probe (it can replace one of the two probes connected to the multimeter) with a button brought out to the finger grip area. It is a simple thing but means that eyes and both hands can be focussed on the circuit or device under test. Once the operator is ready to capture a measurement the button on the finger grip area is depressed and start and stop beep notify when the signal has been stable for a sufficient amount of time (a fraction of a second) to capture a value reliably. Helpfully the measurement range and the timestamp is captured and recorded too. Then you can move on to the next measurement, at no point losing focus from the testbed. The rubber button is squidgy and is like the ones on TV remote controls, but it is clear when the button has been successfully pressed through the audible beep. Without the beep I’m not sure I could trust the button.
The Remote Switch Probe button is brought out to a circular blue connector and it mimics the function of a button on the body of the multimeter.
Another use-case would be to quickly go through a batch of components to perform some manual binning. I tried it with LED forward voltage measurements for a batch of ten. Technically the remote switch probe can also be used just as a remote switch if you only plug in the blue connector, and you can then plug in your own test probes, for example tweezer probes which can be used single handed.
The logging capabilities on the U1282A multimeter itself are very sophisticated and it is possible to log data at timed intervals or whenever a button is pressed or on certain events (like max/min). The in-built multimeter memory is pretty good (10,000 data points for the more useful interval or event/remote switch modes). If you’re using the PC software then there is no need to log the remote switch triggered data into the multimeter memory; it can be recorded directly to the PC with a practically unlimited number of data points.
These (non-high-speed) logging capabilities will be investigated further later. The high-speed logging will form part of this blog post.
Limits
It is possible to set up a few different types of limits (for example upper and lower) and upon occurrence the PC will beep, and can also send you an e-mail. This functionality worked well but the boxes for the thresholds did not seem to handle exponents (E characters) which are useful when dealing with extremely small or large values.
Voice Alerts
A voice feature allows the software to repeatedly speak the current measured value through the PC speaker. It could be useful when your eyes need to focus on the probes and not the display.
Report Generation
There are a variety of reports templates including tables of data and a graph and even a histogram capability, and it will export to Word or PDF format.
High Speed Data Logging
The High Speed feature was claimed to support up to 10Hz update rate, and it does support that across all the measurement types including voltage, current, resistance and capacitance and all the ranges for them. The captured data at this high speed is very clean; there is the occasional misreading but this can be filtered out. In a more than 8 hour period, about 18 resistance measurements were misreadings out of 300,000 data points. (It was subsequently found out that the misreading was due to being in auto-range, where the meter needs to do a refresh occasionally and that involves it changing the meter setting. The solution is to place it in a manual range prior to starting the data logging, and then there are no such misreadings. Note: Keysight are considering forcing the range to be manual for the logger software as a possible future enhancement). The resistance of a thermistor placed in a room was measured over an 8 hour period and the graph of the results is shown in the image below.
The granularity and precision allows for some interesting experiments that I never thought possible with a multimeter. It would be perfect in a science classroom along with the software displayed using a projector.
By placing a thermistor inside a glass jar to isolate it from temperature fluctuations (e.g. due to convection currents) in the room and then using a laser pointer to heat the thermistor, sub-mW power levels can be easily observed.
The Kensington laser pointer was a Class 2 device Probably a few tens of uW is observable with the U1282A connected to a thermistor.
Long Duration Data Logging
As mentioned there is memory for 10,000 data points on an interval basis built-in to the multimeter. With the extremely long reported battery life for the U1282A (800 hours) it would be possible to capture data for days or perhaps weeks. The battery life was impacted by just a few percent during eight hours of logging to the PC.
It won’t always be practical to have a PC nearby and a PC or external storage is needed for high speed data logging that could be needed for long periods To solve this a short piece of software was written to allow interfacing to the U1282A using any low-cost single board computer(SBC). The fastlog software is available on GitHub and it was tested on a Raspberry Pi 3 (but will work on any platform). To compile it, type
gcc fastlog.c -o fastlog
When run as root user, it will report the battery status and the current configuration and will then proceed to capture data at high speed and timestamp it all.
The captured data will be sent to the display and optionally to a CSV format file. Of course this means the sky is the limit - the captured data could be automatically made accessible from a browser for remote monitoring for instance, with negligible effort.
root@raspberrypi:/home/shabaz/development/u1282a# ./fastlog Keysight Technologies,U1282A,MY55480016,V1.03 Configuration: "RES +6.00000000E+02,+1.00000000E-02" Battery: 91% 1, 05/04/2016 19:08:34.943, +9.86500000E+01 2, 05/04/2016 19:08:35.081, +9.86500000E+01 3, 05/04/2016 19:08:35.218, +9.86500000E+01 4, 05/04/2016 19:08:35.369, +9.86500000E+01 5, 05/04/2016 19:08:35.506, +9.86500000E+01 6, 05/04/2016 19:08:35.656, +9.86500000E+01 7, 05/04/2016 19:08:35.806, +9.86500000E+01 8, 05/04/2016 19:08:35.956, +9.86490000E+01 9, 05/04/2016 19:08:36.106, +9.86490000E+01 10, 05/04/2016 19:08:36.256, +9.86490000E+01 root@raspberrypi:/home/shabaz/development/u1282a#
Summary
The High Speed Data logging capability of the multimeter, and the Keysight software combined with the long battery life make the system fantastic for data logging purposes. By connecting to a Raspberry Pi the data can be collected at remote sites at low cost and backed-up over LAN or WAN.
The standards-based serial interface and SCPI messaging allows for custom software to interface to the U1282A.
Based on the fact that the clean output at high speed was sustained for 8 hours with little battery consumption and that it is possible to write software to save data securely I would have no hesitation to use the U1282A for acquiring data over extended periods for the purpose of testing circuits and products and be reasonably confident that good quality precise data was being reliably captured while I am away and that it could be accessed at any time via the network.
In a classroom environment it is possible to perform experiments such as measuring sub-milliwatt power output from a laser due to the ability to observe trends over time with the real time graphing capability in the Keysight application software.
The U5404A Remote Switch Probe allows repetitive tasks to be speeded up and safer and less error-prone measurements are possible. These benefits are due to being able to focus on the circuit under test.and having the capability of capturing data when it is stable for a number of sample periods and direct capture into a table.
The Excel and CSV export provides for great flexibility in the software tools that can be used to display or post-process the measurements.
Thanks for reading.
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