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Automated calibration of non-automated devices


Used by field technicians all over the world, digital multi-metres (DMMs) are a standard diagnostic tool for testing electrical values. These handheld devices need to be calibrated periodically to ensure they remain accurate and reliable, but many DMMs are not equipped with a means of communication, i.e., they have no port for USB, RS232 or similar standards. This meant that calibration was undertaken manually, with technicians required to manipulate the devices, read values on the LCD screen, and record the results. Recently, this time-consuming process was completely reimagined by the design of the first DMM calibration robot.

Rethinking automation

Automated measurements have been possible for many years through the introduction of instrument interfaces such as the GPIB and programmable software such as Fluke MetCAL. Automated Test Equipment (ATE) enables faster measurements while maintaining accuracy and removes the potential for human error. However, devices without an interface remain reliant on an operator to make settings and interpret and record results. Until now….

Trescal, along with Thinkbot Solutions and Linestar Automation, developed a robot that precisely mimics the physical movements of technicians. 

“When we initially came up with the concept, many people thought it was laughable”, says Adam Webb, Regional Technical Manager, Americas, at Trescal. “The calibration process for these DMMs can only be carried out by turning knobs, pushing buttons and visually observing and recording results – so how could it be done without human intervention?” 

Matt Gypps, UK Technical Manager for Trescal, adds “we know this has been tried before and either failed or was only successful on a limited range of products. A system that can be used for any shape or size of handheld DMM is a real breakthrough for Trescal and the UK.”

First launched in Trescal’s Dallas facility, the DMM robot is composed of a mechanical arm with 6 joints, allowing it to articulate in multiple positions compared to a human. It can pick up a wide range of tools and apply exact pressure, enabling it to calibrate standard DMMs with extreme precision. Not only can it calibrate the equipment, the robot can pick up the next piece of equipment in the line for calibration enabling up to 14 handheld DMM’s to be processed in each session. The only manual intervention required is to keep the robot’s assembly line stocked with DMMs. 

Once the technician has performed some basic checks and loaded the system, the measurement process, and certificate production are entirely autonomous. This not only reduces the calibration time and minimises errors, but the technician can invest their time in more challenging activities. 

Deployment of the robot in the UK

Trescal’s Stevenage branch was picked for the UK launch of the robot as the branch already had four manual systems in operation. Calibration requirements are similar around the world, but not the same. The system had to be programmed to meet the stringent requirements of the UK market and pass a UKAS assessment to enable it to be used for accredited calibration service per the requirements of ISO 17025:2017.

Thanks to the flexibility of the design, the system can be used to calibrate any handheld DMM. Physical Digital, the latest acquisition from Trescal, scan each DMM using their 3D structured light measurement solution to add accurate dimensions to the nest template, which is then printed on a 3D printer in the laboratory. This custom carriage fits snug around the device and enables it to be loaded on to the conveyor. Locations of the DMM terminals and controls are all preprogrammed to enable full autonomy of both switch rotation and cable placement.

Benefits of automation

After two years of use in Trescal’s Dallas Branch and feedback from proof of concept, the results show that the robot calibrates just as precisely as highly-trained technicians. The time required for calibration is roughly the same (between 18 and 35 minutes per DMM, depending on the complexity of the device). Still, the real benefit is that the robot frees up technicians to concentrate on more demanding metrology tasks. Technicians no longer have to spend much of their day doing what is essentially routine calibration work and can now focus on their development in other areas.

In addition, the robot can carry on working outside usual shift hours which allows for work to continue after staff have left for the day, provided DMMs have been loaded on the system.

Matt Gypps explains, “We have proven using a robot does not have any negative impact on the quality of our measurements. It has allowed for more time to be spent focusing on future innovations.”

Sharing knowledge

Having demonstrated successful improvements for the Stevenage laboratory, Trescal is now able to deliver DMM calibration to other parts of the UK via their transportation network.

DMMs are designed differently; therefore, it is necessary to create a separate configuration file for the robot each time it calibrates a new DMM type. The file contains details about the device, such as the positioning of dials and input jacks, or the size of the screen. The files can be shared with users of similar robots in other Trescal laboratories in the UK or in any international laboratory.

“We wanted the configuration process to be simple, so technicians didn’t need programming skills”, explains Adam Webb. “That’s why we developed the robot with partners who were experts in LabVIEW and could deliver a user-friendly interface.” Thanks to the work of Thinkbot Solutions (programmatic design and robot integration) and Linestar Automation (mechanical and electrical systems), the robot can be configured to operate on a new DMM by anyone with basic Excel spreadsheet skills. Each new configuration file can then be shared across Trescal’s facilities.”

Inspiration for further applications

Since the robot automates physical actions and translates operations into measurements, the possibilities are endless. “Now that the robot is embedded and has successfully passed a recent UKAS assessment, we are investigating the potential to use it for other manual calibration activities in a number of parameters”, says Matt Gypps. “The potential is exciting and no longer just a concept.”


This article was previously published in the BMTA Newsletter but has recently been updated and revised.