Typical Variable Speed Drive Faults and How to Troubleshoot Them

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 […]

By |2020-05-07T10:55:25-05:00September 24th, 2019|Uncategorized|0 Comments

Flow Control Valves versus Variable Speed Drives – Which You Should Choose, and Why


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.

But along with that long life can come years of lost opportunity costs – the opportunity being employing variable speed drives to reduce energy use on an ongoing basis. Variable Speed Drives (VSDs) – also referred to as Adjustable Speed Drives (ASDs) or, in the case of driven AC motors, Variable Frequency Drives (VFDs) – […]

By |2020-05-07T10:55:25-05:00August 28th, 2019|Uncategorized|0 Comments

Calculating Forced Air Cooling for Control Panels – A Simple Formula for Longer Lasting Controls

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.

Fan air flow thru the enclosure
Filtered Fan Intake and Exhaust – c/o Pfannenberg 2016

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

By |2020-05-07T10:55:25-05:00August 6th, 2019|Uncategorized|0 Comments

Variable Speed Drives – Myths and Facts

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 […]

By |2020-05-07T10:55:25-05:00July 16th, 2019|Uncategorized|0 Comments
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