Frequency Aliasing in Digital Storage Oscilloscopes (DSO)

Digital Storage Oscilloscopes (DSOs) have become extremely popular and affordable due to improvements in Analog to Digital conversion circuitry. DSOs have all but replaced traditional analog scopes on most workbenches and in schools. These new DSOs are extremely powerful but the user must be aware of potential measurement errors inherent in any digital sampling circuitry.

Since these scopes are based on digital technology, the analog signal that is applied to the oscilloscopes input terminal is sampled at discrete time intervals and converted to a digital value so that it may be processed and displayed.

Sampling theory requires that a signal be sampled at a rate of at least twice the frequency of the signal that is being measured. But to obtain an accurate representation of the signal this number should be at least 5 and preferably more than 10 times the frequency of the signal. At low sampling frequencies it is easy to be misled by the waveform displayed on the oscilloscope screen. Therefore DSOs, unlike their analog counterpart, could potentially display an inaccurate display of the signal. For instance if the sweep time is reduced to an extremely slow rate, the displayed signal appears to be at a significantly lower frequency that the actual value.

To check for frequency aliasing, the sweep rate should be momentarily changed to see if the apparent frequency of the waveform changes. The measurement feature of most modern Digital Storage Oscilloscopes can also serve as a validation of the actual signal’s frequency. This frequency (or period) value should be compared with the time/div setting of the Horizontal axis.

It is important for the user to understand this anomaly of digitally sampled test equipment, so that the displayed waveform may be accurately interpreted.

Soldering Iron Troubleshooting

(Note: Never attempt to service your soldering iron unless it is unplugged and completely cool.)

If you’re having issues with your soldering station or soldering iron, you may need a replacement heating element. These heating elements are made of resistance wire that is snugly wound around a metal spool. When the heating element fails, the soldering iron can no longer produce heat.

If, however, the soldering iron is still generating some heat, the issue is probably the soldering iron tip. When the tip isn’t properly maintained — which is to say kept clean and regularly tinned — oxides will begin to accumulate on the shank’s surface. These contaminants must be removed or they will inevitably hinder transfer of heat from the heating element to the tip of the soldering iron.

Once your soldering iron has cooled, remove the tip and gently abrade the shank’s surface as well as the inner wall of the heating element. Ensure that the tip is well seated on the soldering iron, so that the transfer of heat is as efficient as possible; this will also help prevent premature heating element failure. If for whatever reason you’ve failed to maintain the soldering iron tip, you should consider buying a replacement tip.

The majority of soldering irons run on electricity and, if the circuit is broken, the electricity will no longer work. If your soldering iron isn’t producing any heat, it is likely because of a break in the electrical circuit, resulting from either a faulty connection in the iron or heating element failure.

The proper course of action in this case is to check the electrical connections as you disassemble the soldering iron; these connections can come loose over time. Then perform a continuity test of the heating element to test whether the element is still functional.

If all electrical connections were good but you registered no continuity, your heating element will need to be replaced. If the electrical connections were good and the heating element registered continuity, your soldering iron may have a short and will likely need repairs. If the heating element registered continuity and you noticed a loose or faulty connection during disassembly, secure the electrical and physical connections while reassembling your soldering iron and it should operate properly henceforth.

Soldering 101 – An Intro to Soldering

Soldering is required in all electronics manufacturing and repair operations. It can be applied to very small components on Printed Circuit Boards or on larger electromechanical assemblies. The techniques are similar but the soldering station, tip, and solder type may be different for each application.

The basic procedure involves applying a sufficient amount of heat the two surfaces being joined together. This could be a component lead and a PCB, or a wire lead and a metal terminal, like those found on a switch or another wire termination. The amount of heat required will be dependent on the thermal mass of the materials and the type of solder being used.

A small component lead and PCB pad will normally require less heat than a large gauge wire and a heavy terminal. However, some PCB pads may be attached to a large Ground or Power plane and therefore would require a higher amount of heat. In general the largest tip possible should be used for the soldering operation. This tip may still be quite small for a small surface-mount component.

The materials that are being soldered together must be both clean and free of contaminants. Some possible contaminants are dirt, grease, oil, rust and oxidation. If any contaminants are present they should first be removed if possible, before the soldering operation is attempted. Flux, which performs a final cleaning of the materials as the solder is applied, is normally present in the solder. Additional flux is sometimes required for difficult surfaces and when parts are being un-soldered for replacement.

To prepare the soldering iron for the soldering operation, the tip should be cleaned and tinned to provide an optimal solder joint. The soldering station temperature is adjusted to a value that is sufficient to melt the solder being used. This value must be determined experimentally for the reasons mentioned above. The hot tip is applied to the junction of both surfaces (i.e. component lead and PCB surface) and held there for several seconds before applying the solder to the junction. The junction of both surfaces must be allowed to melt the solder for an ideal solder joint. The solder should NOT be applied to the soldering iron tip to produce the connection. Excessive heat and time will damage the component and PCB, and insufficient heat and time will produce a cold solder joint.

Quality solder joints are a combination of proper technique and proper equipment and materials. The technique is a learned process which is optimized through experience.

Measuring Soldering Iron Tip Temperature

You should periodically check your soldering iron tip temperature as a part of your process control system to ensure that it is operating within its specifications and meets/exceeds defined tolerances. Please note that when measuring the temperature you must figure the tolerances of both the soldering iron or station and the measuring device into your measurements, because the tolerances will stack. When measuring soldering iron tip temperature you can account for the tolerance stack using the Root-Sum-Square method.

There are a variety of tip thermometers and station testers for measuring the actual operating temperature of your soldering iron tip. This blog will focus on testing with a tip thermometer. Make sure the device you’re using has a valid calibration certificate with acceptable traceability.

You should also take precautions to mitigate unintentional measurement errors. The first way to avoid error is to take your measurements in an area free of air currents or drafts (for example, from an air conditioner or a ceiling fan). Also, replace sensors every fifty or so times you take measurements: sensors oxidize as you use them and, as a result, they conduct less heat over time, which in turn reduces the accuracy of your measurements.

Furthermore, the same person should always take the measurements under the same conditions to avoid any errors resulting from changes in conditions or measurement techniques. Before testing you should clean the soldering iron tip so that it is free from oxidation and other deposits that can alter your tip temperature measurement and reduce accuracy of the reading. Place the soldering iron tip on the sensor of the tip thermometer and apply a small amount of solder as you would when soldering.

Hold the soldering iron tip horizontally with regard to the sensor and minimize movement to ensure maximum contact between your soldering iron and the sensor — an angle or movement can and often does reduce the tip thermometer’s accuracy.

Press the soldering iron tip to the sensor and wait long enough for the temperature reading to stabilize at its highest point — this is especially important if your tip is narrow or sharp. Some tip thermometers and station testers have a “max hold” feature which will display only the highest temperature reading. Repeat the measurement three times in the same position and record the highest tip temperature. Use this number to discover whether your soldering iron tip is operating within its specifications and meets/exceeds tolerances for accuracy and stability.

Soldering Tips for Beginners

If you’re new to soldering there are some things you should understand before you get started. Don’t just jump into you first project: practice on scrap first. Chances are you have an old radio or some other piece of electronic equipment with wiring and electronic components that will allow you to hone your soldering and desoldering skills.

Newer electronic equipment will be less useful to you because it will consist largely of surface-mounted components, but older electronics will have a ton of wiring and components within that will enable you to practice without breaking everything with one bad connection. After you’ve had some practice you can move onto, for example, faulty cables or simple wiring (such as replacing a potentiometer). Once you grow comfortable with basic soldering tasks you’ll be ready to tackle bigger and more demanding projects.

Always remember to heat the work — not the solder. Rather than applying solder to the soldering iron you should heat the part and then touch the solder to the heated part, letting it flow over the connection on which you’re working. After the connection is well coated you’ll remove the solder before removing the soldering iron. Let the connection cool completely.

Be cautious when soldering PCB-mounted components and IC chips: excessive heat will damage or break them. Instead of soldering the component’s legs directly to the board, try soldering a socket to the circuit board and then insert the component into the socket.

You should always solder in well-ventilated workspaces. You never want to inhale solder smoke, especially if it’s lead solder as a result of its toxicity. It’s best to use protective equipment as well because molten solder can splatter; use goggles or safety glasses.

Don’t solder the plug until you’ve made sure that you’ve put the the plug or housing/shell on the cable. You don’t want to have to desolder the plug, cover it, and resolder. Always double check before soldering.

The process of soldering will be much easier if you tin the wires or the ends of the component’s wires first. Start by heating the individual parts, apply a bit of solder, and let it cool. You should also tin the soldering iron tip and keep it clean. Simply wipe the tip across a wet sponge a few times. Don’t wait until your soldering iron is covered by contaminants. Buildup hinders heat transfer.

Lastly, don’t start soldering until you’ve planned what you’re going to do. Measure twice and cut once.

What Is an Inspection Camera?

An inspection camera, or borescope, is an instrument that functions like a camera, microscope, or telescope: it enables you to observe areas that are too cramped, too far away, or entirely out of reach. An inspection camera has a black-and-white or color display — some of which are detachable for remote viewing — that attaches to a flexible shaft with a camera at the end. The camera often has several LED lights to illuminate the work area. Once the camera shaft is maneuvered into position, you can observe what the camera “sees” on the inspection camera’s display.

British physicist Harold Horace Hopkins invented the rod lens endoscope, the ancestor of the modern inspection camera. Hopkins’ invention enabled surgeons to conduct less invasive procedures by way of so-called keyhole surgery. Since such borescopes allowed one to see bones, muscles, and internal organs, sizable incisions could be avoided, making certain surgeries easier and speeding up recovery times for patients.

There are a wide variety of inspection cameras that cater to several disparate jobs. When an inspection camera has a flexible shaft — also known as an insertion tube — it is referred to as an endoscope or fiberscope, which are often used in medical and veterinary applications: angioscopes are used on hearts, bronchoscopes for lungs, colonscopes for colons, otoscopes for ears, and gastroscopes for stomachs.

In addition to medical applications, inspection cameras have myriad industrial applications: automobile and aircraft mechanics use inspection cameras to view engines’ interiors; electricians, plumbers, and HVAC technicians use inspection cameras to determine where to run pipes and wires as well as to check for blocks and breaks; exterminators use inspection cameras to examine pests’ hives, nests, and tunnels; and locksmiths and law enforcement routinely use inspection cameras. Inspection cameras are also very popular for home improvement among do-it-yourselfers.

Some inspection cameras have the ability to capture still images and record video using an SD card, making them especially useful for documenting what you find. Certain inspection cameras feature digital zoom as well as image rotation for improved observation. Whether you are an amateur or a trained professional, a quality inspection camera can be just the tool you need.

Use a Digital Panel Meter (DPM) to Measure AC Voltage

Digital Panel Meters (DPMs) are strictly DC meters due to the digital circuitry used. Oftentimes it is desired to utilize a DPM to measure AC voltages to take advantage of the improved accuracy and readability of a DPM. This application note will describe the method to accurately display AC voltage values on a DPM.

The CX102A Digital Panel Meter from Circuit Specialists is ideal for this application, as it is designed to use in a system that has the measured signal isolated from the power supply voltage. The application is for a 0-120 volt AC meter powered by an external 9 volt battery. This application could also be powered by a “wall-wart” type of AC adapter if desired.

Like all Digital Panel Meters, the full scale range of this DPM is 200 mv full-scale. To use the DPM to measure AC voltages, the AC voltage must be converted to DC by a rectifier diode. The output from the rectifier diode will be a “pulsed” DC voltage and may produce undesired fluctuations in the reading on the DPM, so we will add a small filter capacitor across the rectified output voltage. The voltage rating of this capacitor and the rectifier diode must be high enough to handle the voltage levels present in the circuit. To be safe, we will use a rectifier diode and capacitor rated at 250 volts or higher. Since we are using a single rectifier diode to convert the AC into DC, we will have to choose our divider resistors appropriately to compensate for the effects of the half wave rectifier operation. Since the AC power line voltage is rectified by the series diode, the voltage applied to our DPM is the peak value of the 120 volt line voltage which is 120 V multiplied by 1.414 .

Vout = Vin X (1.414) = 120 X (1.414) = 169 V (DC)

This is the actual DC voltage applied to our voltage divider resistors, so we will use the voltage divider formula to determine the required resistors to produce the correct reading on the DPM.

To keep the calculated values within a range that is readily obtainable, we will use 10 Meg ohms as the maximum series resistor value. We can then calculate the shunt resistor for our voltage divider network using the voltage divider equation

Vout/Vin=Rshunt/(Rseries + Shunt) rearranging we can solve for the required

Use Rseries = 10 Meg Ohms

For 0-120 Volts, Rshunt = 7.2 K ohms (use 7.5 K ohm)

We will also need to connect pin 3 to pin 4 (for proper decimal point display).

Note that the voltage value displayed on the meter can be fine-tuned by adjusting the trimmer potentiometer on the back of the DPM.

This application note has shown how a Digital Panel Meter may be used to measure and display AC voltage values. The connection diagram is shown below.

Note that pins 8 & 10 are shorted together and connected to the Neutral connection of the AC voltage that is being measured. Rshunt will be connected across pins 7 & 8 and Rseries will have one end connected to pin 7 and the other end to the voltage that is being measured.

 

Measuring Current with a Digital Panel Meter (DPM)

Digital Panel Meters (DPMs) are voltage measuring devices unlike Analog meters which are current measuring devices. When current measurement is required, the current must be converted to a voltage if a digital value is to be displayed. This application note will describe the method to accurately display DC current values on a DPM.

There are several methods that can be used to convert current to voltage such as Hall effect devices and shunt resistors. Since shunt resistors are the easiest to use and provide the greatest amount of accuracy, this technique will be examined. The shunt resistor is placed in series with the applied current which causes a voltage drop to occur across the shunt. To minimize the voltage drop in the circuit, the smallest resistance value possible should be chosen. This value depends on the maximum current value that will be encountered. For relatively small current values (below 1 Amp) a 0.1 ohm shunt resistor should perform adequately. This value will minimize any loading on the circuit but will still produce a reasonable reading on the DPM. If higher current levels will be encountered, a 0.01 ohm or lower value should be used.

The CX102A Digital Panel Meter from Circuit Specialists is ideal for this application, as it is designed to use in a system that has the measured signal isolated from the power supply voltage. The application is for a 0-1 Amp DC meter powered by an external 9 volt battery. This application could also be powered by a “wall-wart” type of AC adapter if desired.

Like all Digital Panel Meters, the full scale range of these DPMs are 200 mv full-scale. To use the DPM to measure current, we will choose our shunt resistor to assure that no more than 200 mV is developed across it. We will also set the Decimal point jumpers accordingly to indicate the correct Amp reading. For instance, if 1 Amp is the full scale reading desired, we will use the 0.1 ohm resistor and set the decimal point jumper to show three digits to the right of the decimal point. We must also determine the correct power rating of the shunt resistor by using the ohms law power formula P (Power)=E (Voltage) X I (Current).

P = V max X I max = (0.200) X (1.0) = 0.1 Watt

So we should use a 1/2 watt 1 % resistor to be safe.

We will also need to connect pin 3 to pin 6 (for proper decimal point display).

Note that the current value displayed on the meter can be fine-tuned by adjusting the trimmer potentiometer on the back of the DPM.

This application note has shown how a Digital Panel Meter may be used to measure and display DC current values. The connection diagram is shown below.

Note that pins 8 & 10 are shorted together and connected to the Negative end of the shunt resistor. Rshunt will be connected across pins 7 & 8 and will be connected in series with the load.

Replacing the Heating Element of Your Soldering Iron

Your soldering iron works by heating the element that transfers heat to the tip. A defective heating element doesn’t allow the soldering iron to function properly and must be replaced in order to correct the malfunction, thus returning the soldering iron to its ordinary functional state. You’ll need a replacement heating element and some tools including wire cutters, a spanner wrench, and needle-nose pliers. Let’s take a look at the process of replacing the heating element of your soldering iron.

First you’ll unscrew the handle from your soldering iron by hand and pull the handle from the soldering iron. Then unwind the protective tape around the soldering iron assembly. Keep the tape for later use. After removing the protective tape you’ll see two connectors; twist the connectors’ ends and separate the the two wires from the connectors. You won’t need tools for any part of this process.

Next you’ll clip off the pair of metal lugs beside the connectors with your wire cutters. Trash the metal lugs. There is a nut at the end of your soldering iron assembly that you’ll turn counterclockwise with your spanner wrench. Finish unscrewing the nut by hand and then unscrew the ring on the end of your soldering iron.

Use the jaws of your needle-nose pliers to clamp the heating element within the end of your soldering iron. Now you’ll be able to pull the heating element from the soldering iron with your needle-nose pliers. Go ahead and trash the old heating element.

Insert your new heating element with the wire end first into the soldering iron assembly. Then screw the ring back on. Use your fingers to separate the two leads of your replacement heating element. Tighten the nut by hand and finish tightening the nut with the spanner wrench. Don’t overtighten the nut: your soldering iron naturally expands and contracts during use.

Insert the heating element’s leads in the soldering iron’s connectors and wrap the protective tape around the the connectors. The last thing you’ll do is screw the handle back on the soldering iron.

Be sure to keep the soldering iron tip clean and free of dust and other contaminants so that your soldering iron will last as long as possible.

How to Desolder

Although soldering is a very important skill to have, desoldering is important as well and, in some cases, can be be an even more useful skill. Let’s take a look at the basics of desoldering.

You need a soldering station or iron and a device for removing solder to desolder. Your soldering iron will be the heat source used to melt the solder and soldering irons between in fifteen and thirty watt range will be sufficient for most circuit board work — higher wattage irons introduce the risk of damaging components or the board itself. Do not use a soldering gun, which passes an electrical current through an internal wire that carries stray voltage which may damage your components and board.

The two types of desoldering devices are vacuum pumps (solder suckers) and desoldering braid (desoldering wick or solder wick); both are a means to the same end, so use whichever you prefer, but it’s beneficial to learn how to use both, given that one or the other may work better for a particular situation.

You won’t need to do much surface preparation when desoldering. Simply ensure that all grease, varnish, and glue are removed from the joint before heating, otherwise the tip of your soldering iron will be fouled quickly.

Because desoldering can release fumes that are detrimental to your eyes and lungs, be sure to work in a well-ventilated area. You should also wear eye protection. Be aware that molten solder can splash and burn you.

When you’re ready to desolder you’ll apply heat by pressing the soldering iron’s tip against the component’s lead and the circuit board. It should only take a few seconds to thoroughly heat the component but larger components or soldering pads can take longer.

Vacuum pumps, which look a bit like syringes, have a spring-loaded plunger and a button to release the plunger. You push it down and, when you want to suck up the solder, you position the device’s nozzle over the melted solder and press the button, thus creating a vacuum that sucks up the solder. You will probably have to repeat this process multiple times to remove all the solder.

Desoldering braid has no moving parts. First heat the braid by leaving the wick over your soldering for a few seconds; once it’s hot you’ll feel the braid start to slide. You’ll then place the braid over the joint and heat it. You should be see the solder begin to flow into the desoldering braid. Unlike desoldering with a vacuum pump, you shouldn’t have to repeat this process. After a section of braid is filled with solder it needs to be replaced: simply cut the used section from the spool.

A good way to combine both desoldering methods is to remove as much solder as you can with the vacuum pump and finish up with desoldering braid. After you’ve finished you may want to clean the desoldered area to remove any leftover resin. There are a number of commercial products available for this purpose.

Simply smart circuitry since 1971.