In our last article we looked at a few of the possible sources of electronic equipment damage due to power transients. In this article Jim and Chuck will further investigate ways to troubleshoot and correct these transient conditions to protect electronic equipment.

Although there are four types of power anomalies, there are three ways that transient voltages can enter an electronic system (including scales):
•The power source
•Peripheral ports
•Electrostatic Discharge (ESD)

The basic goal of any protection device is to divert the excess charge along a path to ground that does not include any of the sensitive electronic components that will suffer damage. This is done in a number of ways and the methods are tailored to the source of the excess voltage.

The power source

Most electronic scales need a source of AC power. Some battery-operated units can be exempt from this type of disruption, but during their charging cycle, they become susceptible, sometimes even if the unit is turned off. Most electronic devices use a power supply that converts the raw AC power into a lower DC voltage. A linear power supply can shield against passing many transients through to the circuitry, but more modern switching power supplies can block many common transients also. The power source can contain any combination of surge (overvoltage for one half cycle or longer), sag (under voltage for one half cycle or longer), or transient, over or under voltage that is very short in duration (less than one half cycle), but can contain very high voltage peaks.

Most modern electronic devices are internally grounded and protected from a static electricity discharge from any outside surface of the device. The problem becomes greatly magnified when either the grounding is subverted or the case is opened. The use of a three-to-two wire adapter on the AC cord is one of the most common ways this is accomplished. The ground pin on an AC cord and receptacle is provided to do just that—connect the device to a legitimate ground (see sidebar “Respect for the AC receptacle”).

If an extension cord is used, be sure that not only is the grounding pin intact on both ends, but that they are connected. Use an ohmmeter to confirm this before plugging in either end of the extension cord. A simple method to check the basic wiring and to ensure that the ground, neutral and hot wires are connected properly is to use a simple tester as shown below. These are available in hardware and electrical supply houses and are quite inexpensive. Any problems that show up using this test require immediate action. NO EQUIPMENT OF ANY SORT should be plugged into any receptacle showing a wiring problem. Remember this device will only tell you if the wires are connected properly, not if the quality of the connection is good or even adequate. Once the wiring has been tested for correctness, the problems of surges, sags and transients need to be addressed. These will require more rigorous testing. All three can be monitored using a device which plugs into the receptacle and monitors and collects information such as the voltage, frequency and any transients outside of specified norms. The data is stored and can be downloaded later into a computer for analysis. Click here to read the rest of part two.

This is the first of a three part series of posts that discusses electronic components and static electricity courtesy of Rice Lake’s Jim Daggon, senior product manager, and Chuck Crowley, senior technical support, who use static control wrist straps and use a dissipative work surface to protect sensitive components and circuits from ESD and once you read these three articles, you will probably be interested in doing the same.

Zap! Unseen, unfelt and unheard, electrostatic discharge (ESD), commonly known as static electricity, is damaging millions of dollars’ worth of electronic components every year. Electrostatic discharge is an electrical charge transferred between bodies at different electrostatic potential. “Static” electricity is the buildup of a charge on one object without a circuit for the current to flow through. When the charge builds up to the point where the voltage can “jump” the distance to a lesser charged object, it discharges with a spark. Once that spark occurs, the circuit is completed and current flows along the path of the spark. Lightning is the largest static electricity charge most of us will ever see. But we’ll discuss lightning more later.

That ZAP! you get when you shuffle across the rug in the winter and touch the TV can be annoying, but the voltages that build up can be deadly to today’s electronics. Quite often that damage is unseen. A zapped electronic device may work when it leaves your hands, but more than likely, its length of service has been reduced significantly. You cannot feel ESD below 3,000 volts, hear it below 5,000 volts, or see the spark below 10,000 volts. Many electronic devices can be damaged by ESD of well under 1,000 volts—EPROMs can be damaged by only 100 volts!

If this sounds hard to believe, look at the following stats:

• In low humidity, walking with rubber-soled shoes across a vinyl floor can build up 12,000 volts.

• Pulling tape off a dispenser just 6 inches can build up 4,000 volts.

• Walking across carpet can build up 35,000 volts.

Without a ground path to dissipate the charge, nonconductors like papers, plastics, foam coffee cups, clothing, and people can carry thousands of volts.

While moist air allows charged bodies to slowly drain off an excess charge to ground, dry air inhibits that charge dissipation. Simply adding moisture to indoor air may stop painful charges arcing to your fingertips from light switches in carpeted rooms, but it is not sufficient protection for sensitive electronic components. For this protection, a total system that prevents all damage by static must be in place.

Electronic Equipment Damage—Power Related

Today’s electronic equipment relies heavily on the power supplied to it to maintain its reliability, yet sometimes the power itself causes its downfall. Power for today’s high speed, fast-computing, and full-featured designs are very susceptible to power anomalies that, less than a decade ago, would have been insignificant. In the reel-to-reel tape recorder days gone by, the higher tape speeds were used for higher fidelity, since any noise was then spread over a wider section of tape. This higher speed works against us in today’s microprocessor clock speeds. A single extraneous pulse lasting a mere millionth of a second can disrupt 1,000 clock pulses in a 1 Ghz microprocessor.

Power anomalies come in a variety of types. Four of the more common ones are surges, sags, transients, and faulty wiring. Click here to read the rest of the part one article.