Over the next few columns, we’ll examine some of the more common faults experienced by variable speed drives, their causes, and some ways to resolve them.

Modern variable speed drives (VSDs, a.k.a. VFDs or ASDs) are very reliable devices when installed and maintained properly. However, VSDs can experience faults, alarms, and errors from time to time, just as can any complex electronic component. It is helpful to know how to deal with such issues when they occur. Over the next few columns, we’ll discuss some of the more common faults that might be seen, and how to address them efficiently and with minimal wasted effort. I will be referencing troubleshooting methods recommended by a variety of VSD manufacturers we use, although many of these approaches will be suitable, with minor modifications, for any modern VSD.

Before we begin, let’s cover some general considerations applicable to any troubleshooting process. First, the manufacturer’s manual is usually your best source for determining the problem and what to do about it. Often the manual will have a decision tree or block diagram detailing the specific steps needed to troubleshoot each fault or alarm. This can […]

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Until relatively recently, flow control valves (FCVs; also sometimes referred to as throttling valves) were the most common means of regulating flow in a process line. Over the decades that FCVs have been in use, both control technology and mechanical construction have improved greatly, significantly reducing the process inefficiencies – hysteresis, lag, pressure drop, etc. – associated with these valves. And despite the sophisticated control systems often used to operate them, valves are relatively simple devices. With maintenance properly scheduled and performed they can last a very long time indeed.

Most people are aware that electrical and electronic components are heat-sensitive, and that their life expectancies can be reduced significantly if they are not kept within specified operating temperatures. Typical upper limits for specified operating temperatures are 40°C (104°F); occasionally 50°C (122°F). One common application challenge is maintaining temperature below these upper limits within a control enclosure. There are a number of variables which need to be considered when determining the cooling needed, including the size of the enclosure, its material and finish, its location (e.g. outdoors in shade or sun), and, in general, the variability of the ambient temperature during operating periods. Note that all of these factors are in addition to the the impacts of the internal components and their heat loads; i.e. the heat they give off during operation. Today we’ll examine these factors and look at one cost-effective means for addressing them – forced air cooling, also known as fan-forced air (FFA) or forced convective cooling.

First, let’s look at the formula to calculate the amount of forced air cooling needed. This formula […]

There is a good deal of knowledge, and more than a little misperception, about the use of variable speed drives (VSDs). The term “variable speed drive” encompasses both variable frequency drives (VFDs) used for controlling AC asynchronous and synchronous motors, and DC variable speed drives for controlling DC motors. In either case, determining if and when to use a drive will be much easier once the facts and myths about these controllers are clear. Let’s examine some of the more prevalent ones.

Myth: “My process flow application is already controlled by control valves, so I don’t need a VFD.”

Fact: In many cases, a VFD can more accurately control flow while reducing power consumed by the pump motor. If the flow control valves (FCVs) are being used mainly to throttle flow, you could instead use a VFD to reduce the speed of the motor, thus reducing the flow at the source. The reduced motor speed means less energy consumed by the system; per the Affinity Laws, power consumption (in watts) in a centrifugal pump application would be reduced by the cube of the reduction in speed (see formula below). You wouldn’t even need to remove the FCVs; simply open them fully and […]

In the last article, we spoke about the requirements-based design and engineering that go into the fabrication of a high-quality, custom-built control panel. Much of this necessarily happens “behind the scenes”, well before a panel is assembled, but when you’re in the process of choosing a panel fabricator all you may have to go on is the “look and feel” of examples being advertised. So, whether you’re online searching panel builders’ sites, or in the field reviewing build quality, what should you look for in a quality custom-built control panel? Let’s examine the most common things to watch for.

• Workmanship: They say “neatness counts”, and this is doubly true for control panel fabrication. A clean, well-managed, orderly layout makes maintenance and trouble-shooting far easier, saving time and money. Keys to look for:
  • Components properly anchored and laid out in a logical fashion
  • Wires neatly bundled and routed with minimal interference, and meeting minimum bending radius requirements
  • Clearances maintained for ease of access and adequate ventilation
  • Consistent wire coloring scheme
  • Covers in place and fastened properly

What Makes a High-Quality Control Panel?

A high quality, well-built control panel is perfectly adapted to its function and, when well-maintained, will provide many years of good service. Just as there are numerous applications with diverse requirements, so there are all types and configurations of panels out there. See Fig. 1 for an example.

So how do you recognize a quality panel when you see it, and more importantly, how can you be sure that a panel builder will provide a quality product before it’s built? Let’s take a closer look at the elements that go into quality control panel design and fabrication.

Understanding the Application and User’s Requirements

Quality is not just a reflection of the materials used, but also of the ability of a panel to satisfy its intended purpose. After all, a panel is only as good as its ability to work properly. And that means clearly defining what the panel must […]

Due to often high starting torque, heavy loads, and changing viscosities, mixing applications can be challenging. But with the right torque vector variable frequency drive (VFD) consistent batching, equipment life, and energy efficiency go hand-in hand. Let’s take a closer look at the features and capabilities that make these drives a solid choice for process mixing applications.

Starting torque: A number of factors can influence the amount of starting torque needed to get agitators in motion. The sheer volume of materials to be mixed, and their density, can place a lot of stress on vessel mixing components. Tank design also influences this – factors such as tank geometry, agitator design, baffle design and geometry, hub arrangement, motor power output, and tank temperature control all can affect the torque needed to begin a mixing cycle. And of course, batch variability also is a critical factor.

Modern vector control drives are capable of providing full torque at zero speed, which not only ensures sufficient starting power but also allows for efficient power consumption during starting. Where high torque isn’t needed, the soft-starting capability of these drives can save significant wear and tear on mixing components and gear boxes.

Mixing dynamics: […]

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John Gierich
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