Because a lot of us were thinking about the Rockwell Automation Fair that happened in early November 2012, our October Fluke Plus survey focused on technicians who work in controls and automation testing. We were gratified to receive about 57 responses that provided insight into the challenges of maintaining and troubleshooting automation controls. Although the majority of responses came from the United States, we also had a good showing from Canada, and responses from as far away as Greece and Malaysia. The job titles of the respondents included, as you might expect, many controls engineers, electricians, and I/E technicians. We also heard from a college professor and a few metrologists.
Most of the respondents said they troubleshoot programmable logic controllers (PLCs), programmable automated controllers (PACs), and/or variable frequency drives (VFDs). From there the responses tended to diverge. In addition to the standard PLCs, PACs, and VFDs, the respondents mentioned a wide range of controls that they troubleshoot. Those include motor starters, ultrasonic flow meters, analytical systems, and field instrumentation, as well as robotics, HMI sensors, and temperature, relay logic, pneumatic, and direct digital controls.
How often are new control devices disruptive?
When asked whether they had ever encountered problems downstream after a new control device was introduced, nearly half of them answered “yes.” A few cited problems like broken wires or mis-wired controls. A few others had run into bad controllers. From there the answers became more individualized.
A calibration program manager noted problems with loop power loss and calibration and impedance issues when testing 1V to 5V and 4-20mA signals. A master electrician, who tests a wide variety of controls including ac and dc drives, networked devices, sensors, temperature controls, programmed systems, and motor control centers (MCCs), said the problem he encountered most often was “a communications failure between the new control and existing loads.” Another electrician, who troubleshoots relays, adjustable frequency drives, resistor banks, and motors, identified his most common problem as fluctuating or intermittent power. An electrical controls engineer who troubleshoots digital and analog input and output signals on temperature controls, process equipment, and electrical systems found that sometimes “power company capacitor switching caused regular ac variable frequency drive trips.”
Problems multiply when new meets old
An instrumentation and electrical (I&E) technician who troubleshoots pneumatic controls described a problem with a new dissolved oxygen meter controlling a variable frequency drive on an aeration basin in a waste treatment facility. “The dissolved oxygen meter wouldn't get to our controlled variable set point. We were able to reach it before with the old meter so it has to be constantly calibrated; it just keeps trailing off.”
One I&E technician who works with analytical systems and field instrumentation sometimes has to deal with incorrect process automation configuration at the distributed control system when new controls are added. Another instrument technician mentioned that when he “changed a process from actuated valves to VFD control, the PID/tuning took a long time.”
Along those same lines, an E&I technician and reliability inspector who troubleshoots distributive control outputs and control valves said he found that “issues hidden behind the variability of older analog equipment became more pronounced after digital smart devices were installed that operated with tighter variability coefficients.”
The primary troubleshooting tools
We asked respondents what test tools they use to troubleshoot these problems, and it turns out that all but about seven of the respondents use a digital multimeter and/or clamp meter as their primary troubleshooting tool. The next most often mentioned test tools were power analyzers and ScopeMeter® portable oscilloscopes.
We thank all of those who responded to the survey and appreciate your filling us in on some of the common challenges you deal with on a day-to-day basis.