Fullscreen HTML5Med Res (??MB)HTML4

By JOHN CLARKE Most readers would know that you can obtain small ultrasonic cleaners for jewellery and similar small items. So why not a much larger version? It would be great for cleaning automotive and other mechanical parts, fabrics which cannot be machine washed, ornate bric-a-brac and a host of other hard-to-clean items. A nyone who has ever needed to clean the parts for a carburettor, differential, gearbox or any other greasy and intricate parts must have often wished for an easier way. Generally you dunk the parts in a container of kerosene, dieseline detergent or whatever, to soak for a while and then you return to the task with various brushes and implements to scrape off the grease and other gunk. It is a dirty and tedious task. But what if you could dispense with all that brushing and scraping? If you could just drop the components in a tank of suitable solvent, press a button and then come back later to remove the parts in sparkling clean condition? Our ultrasonic cleaner is designed to do exactly that job. It uses a high power piezoelectric transducer and an ultrasonic driver to literally blast away the dirt and grime with ultrasonic energy. The solvent might be kerosene or hot water and a wetting agent such as a detergent. At low drive levels the solvent conducts the ultrasonic signal throughout the bath. At higher power levels, the ultrasonic wavefront causes cavitation which causes bubbles to form and then collapse. This is shown in Fig.1. As the wavefront passes, normal pressure is restored and the bubble collapses to produce a shock wave. This shock wave helps to loosen particles from the item being cleaned. The size of the bubbles is dependent upon the ultrasonic frequency and is The two “halves” of the project: the controller at left and the ultrasonic transducer, potted in a length of pipe, at right. 58  Silicon Chip siliconchip.com.au Feature s • 12V plugpac k powered • Automatic timeout • Adjustable timeout • Start butto n • Rugged tran sducer Cleaning a coffee-stained stainless steel tray in our “bath” (actually an old plastic cistern – see page 65). You can’t see the bubbles being generated in this photo – they’re too small – but they are certainly there. WARNING! This circuit produces an output voltage of up to 800V peak-peak to drive the ultrasonic transducer and is capable of delivering a severe (or even FATAL) electric shock. DO NOT touch the output terminals at CON2, the PC tracks leading to CON2 or the transducer terminals when power is applied. To ensure safety, the PC board must be housed in the recommended plastic case, while the transducer must be correctly housed and fully encapsulated in resin as described in the article. smaller with higher frequencies. Industrial ultrasonic cleaners tend to use frequencies between 20kHz and 50kHz while cleaners for small parts typically use frequencies above 50kHz. Our ultrasonic cleaner sweeps the frequency range from about 19kHz to 42kHz to produce cavitation bubbles of varying sizes. The frequency is varied with an irregular pattern to avoid a constant low frequency sub-harmonic in the cleaning bath or tank. Variation of the sub-harmonic frequency reduces the impact of resonances in small items being cleaned that may otherwise cause them to disintegrate. siliconchip.com.au This variation in frequency also prevents standing waves in the cleaning bath that can produce cavitation in one area but no cavitation in another area. This can lead to irregular cleaning action of a component. Actual power delivered is dependent upon the resonant frequency of the piezo transducer. For the Silicon Chip Ultrasonic Cleaner, maximum power delivered by the transducer is at about 40kHz which is the resonant frequency of the specified piezo ultrasonic transducer. The Ultrasonic Cleaner can be set to run for between 30 seconds and 10 minutes. Alternative sweep pattern An alternative sweep pattern is available that sweeps over a frequency range of around 12kHz, centred on the 40kHz resonance. This produces a higher agitation level in the cleaning bath due to the transducer frequently running through its resonance. This alternative sweep pattern should be for intermittent use only. Which sweep pattern is best depends on the component being cleaned and the type of contamination. The driver for our Ultrasonic Cleaner is housed in a small plastic case. This connects to the piezoelectric ultrasonic transducer itself using a length of sheathed 2-core mains-rated CAVITATION BUBBLE FORMS BUBBLE GROWS IN RAREFIED PRESSURE BUBBLE SHRINKS UNDER RESTORED PRESSURE BUBBLE COLLAPSES CAUSING SHOCK WAVES NEW CAVITATION BUBBLE FORMS Fig.1: the ultrasonic cleaning process. It’s all about causing shock FIG.1 solvent to waves in the cleaning literally “shake off” the dirt and grime. You can do this manually – but the ultrasonic transducer does it 40,000 times each second! cable. The piezoelectric transducer is housed in a PVC fitting that covers and insulates the terminals from accidental contact. This is necessary because the transducer is driven at a high voltage which could cause a nasty shock if you come into contact with it. August 2010  59 12V DC INPUT S2 + F1 3A (OPTIONAL) – 2x 4700 F 16V LOW ESR 100 CON1 A D3 1N4004 WARNING! 2.2k 2.2k A POWER LED1 REG1 78L05 K GND 100 F 16V LED2 100 F 16V D7 A  K +5V OUT IN K RUNNING A  K 100nF A A D6 D5 K K 1 Vdd TIMER VR1 10k LIN 5 100nF GP1 2 X1 20MHz 22pF 3 OUT 22pF 22k K A A D1 ZD1 5.1V 1W IC1 PIC12F675I/P A GP0 10k 4 F1 T1 F3 S2 ZD2 5.1V 1W Vss K Q2 RFP30NS 06LE 78L05 LEDS GND K A A IN OUT 8 A 2010 TO ULTRASONIC TRANSDUCER D G ZD1, ZD2 SC  CON3 S3 S1 F2 A 10 7 GP3 10 F 16V G K Q1 RFP30NS 06LE FTD29 FERRITE TRANSFORMER D4 CON2 D 10 6 IN K START S1 K D2 AN2 The output from this Ultrasonic Cleaner driver circuit is at a high voltage (up to 900V p-p). Avoid making contact with the output terminals (CON3) and the transducer terminals when the unit is running or you may experience a severe electric shock. The transducer must be fully encapsulated to ensure safety. ULTRASONIC CLEANER K D4-D7: 1N4148 A K RFP30N06LE D1,D2: 1N5819 D3: 1N4004 A K G D D S Fig.2: the driver circuit for the piezoelectric ultrasonic transducer is controlled by a PIC12F675-I/P micro. Two oscillation modes are available, the alternative is selected by holding the “start” button down as power is applied. The piezo transducer and housing can be directly immersed in the ultrasonic bath or tank. Alternatively the transducer can be glued to the outside of the bath using epoxy resin for deeper baths. in small increments amounting to 320Hz at around 40kHz. Outputs GP0 and GP1 provide complementary gate drive signals for Mosfets Q1 & Q2. Since these outputs only swing from 0V to 5V, Q1 & Q2 are logic-level Mosfets. Standard Mosfets require gate signals of at least 10V for full conduction but logic-level Mosfets will fully conduct with much less. For the RFP30N06LE Mosfets specified, the on-resistance between drain and source is a mere 75mΩ at 20A at a gate voltage of 3V. The on resistance drops further to around 23mΩ at 20A at the higher gate voltage of 4.5V. The Mosfets are rated at 30A continuous. Q1 & Q2 are driven alternately Circuit details and these in turn drive the separate The circuit of our Ultrasonic Cleaner halves of the transformer primary (fig.2) is relatively simple due to the which has its centre tap connected to use of an 8-pin PIC12F675-I/P microthe +12V supply. When Mosfet Q1 is controller, IC1. This drives switched on, current flows in the piezoelectric transducer its section of the transformer via two Mosfets, Q1 & Q2 and primary winding. transformer, T1. The micro- Power Requirements............... 12V at 2.5A Q1 remains on for less than controller also provides the Transducer voltage................. 250VAC square wave 50us depending on the fretimer and the start functions. Frequency range.................... Main mode is 19kHz to 42kHz quency and is then switched Crystal X1 sets the microoff. Both Mosfets are then off with irregular variation controller to run at 20MHz. for a few microseconds before This frequency allows the Alternative frequency Range...... 34 to 44kHz Q2 is switched on. Q2 is then ultrasonic drive to be shifted Timeout Adjustment................ 30s to 10m switched on for the same du- Specifications 60  Silicon Chip siliconchip.com.au Running indication LED2 indicates when the Mosfets are switching on and off. When Q1 is switched on, diode D6 can power LED2 via the 2.2kΩ resistor from the 12V supply. When Q2 is switched on the LED is driven via D5. When both Q1 and Q2 are off, the LED is not driven. When either Q1 or Q2 are switched off, the high voltage from the transformer primary winding at the Mosfets’ drain can couple through diodes D5 or D6 due to capacitance. Diode D7 clamps the voltage to 0.7V above the 12V supply to protect LED2. OPTIONAL SWITCH S2 (CUT TRACK UNDERNEATH IF USED) 100 5819 100nF D2 22k 5819 D1 S1 F2 Q2 S3 F3 5V1 10150140 F1 100nF 22pF 22pF X1 RE NAEL C CI N OSARTLU START S1 CON3 S2 ZD1 10 IC1 12F675 10k 4148 10 F 2.2k T1 Q1 CON2 LED1 A ZD2 A 4700 F 16V LOW ESR E GATL OV H GI H !RE G NAD 100 F 2.2k REG1 4700 F 16V LOW ESR 5V1 4148 10 D5 LED2 4148 D6 4148 100 F CON1 D7 D3 12V DC IN F1 D4 ration as for Q1 and then both Mosfets remain off for a few microseconds before Q1 is switched on again. The gap when both Mosfets are off is the “dead time” and it allows each Mosfet to fully switch off before the other is switched on. The alternate switching action of the Mosfets generates an AC square wave in the secondary and since the primary/secondary turns ratio is 11.25:1, the secondary winding delivers about 250VAC to the piezoelectric transducer at between 19kHz and 42kHz. Mosfets Q1 and Q2 include overvoltage protection which clamp any drain voltage that exceeds 60V. This clamping is required since a high-voltage transient occurs when the transformer primary winding is switched off. Protection for the gate of each Mosfet is provided using 5.1V zener diodes. Although the Mosfet gate is only driven from a 5V signal, the high transient voltage at the drain can be coupled into the gate via capacitance between gate and drain. The 5.1V zener diodes prevent a higher voltage driving IC1’s GP0 and GP1 inputs which could damage them. Further protection is provided for GP0 and GP1 using diodes D1 and D2, which are in parallel with the chip’s internal protection diodes. These clamp and carry the current if the voltage at these pins goes above about 5.3V. TIMER VR1 TO ULTRASONIC TRANSDUCER Fig.3: component overlay for the Ultrasonic Cleaner. All components (except the start button, timer pot and transducer!) are mounted on a single-sided PC board. If an on/off switch is required, the copper track must be cut between the S2 pins. digital value which is used as a basis for the timeout. The maximum timeout of 10 minutes is set with the wiper of VR1 at 5V, with shorter timeouts as VR1 is reduced. The lowest practical setting is about 30s. When the potentiometer is set to its minimum position, the timer will not run and the Mosfets are kept off. If the potentiometer is rotated to this minimum position during the running of the timer, the timer will also be switched off, turning off the Mosfets. Starting the ultrasonic drive is initiated by pressing the start switch. Normally, the GP3 input (pin 4) is held at 5V via a 22kΩ pull up resistor. When the switch is pressed, this input is pulled to 0V and signals IC1 to run the ultrasonic drive. Timer IC1 also performs the timer function. This switches off all drive to the Mosfets after a preset time period, set by the position of potentiometer VR1. VR1 is wired across the 5V supply with the voltage at the wiper monitored by IC1 at the AN2 (pin 5) input. IC1 converts the voltage into a siliconchip.com.au The completed PC board, ready for insertion into the case. The on-board power switch (S2) is not used here – the two PC pin holes (top left) are empty and the thin copper track underneath is intact. August 2010  61 The voltage waveform appearing the ultrasonic transducer as it is swept over a range of frequencies. In this case it is shown at 20.8kHz. Note the high peak-peak voltage of 600V. When S1 is released, the 10µF capacitor across the switch charges up to 5V via the 22kΩ resistor. Diode D4 discharges the capacitor when power is switched off and the 5V supply rail drops to 0V. 5V power for IC1 is derived from the 12V supply via a 100Ω resistor, reverse polarity protection diode D3 and 5V regulator, REG1. The supply to REG1 is filtered with a 100µF capacitor, while the 5V output is bypassed using 100nF and 100µF capacitors. Reverse polarity protection for the power section of the circuit is via a 3A fuse (F1), along with the integral reverse diode within each of Mosfets. These diodes conduct current through the primary windings of transformer T1, effectively clamping the supply voltage at -0.7V, protecting the 4700µF electrolytic capacitors from excessive reverse voltage. The 12V 2.5A plugpack includes foldback current limiting where current at voltage below 12V is reduced from its maximum rating of 2.5A. With a short circuit the current limit is around 0.5A. The fuse is unlikely to blow and power dissipation in the Mosfets is around 0.35W total. This does not cause any harm to the Mosfets, the transformer or the capacitors. The fuse is included to prevent the PC board tracks from fusing should the transformer be wound incorrectly or if one of the Mosfets fails as a short circuit. Power-on indication is via LED1, powered via a 2.2kΩ resistor from the 12V supply. Construction The Ultrasonic Cleaner is constructed on a PC board coded 04208101 and measuring 104 x 78mm. It is mounted in an IP65 ABS box with a clear lid and measuring 115 x 90 x 55mm. The clear lid allows the power and running LEDs to be seen without having to drill extra holes. The PC board is designed to mount onto the mounting bushes inside the box. Make sure the PC board is shaped to the correct outline so it fits into the box. It can be filed to shape if necessary using the PC board outline as a guide. Begin construction by checking the PC board for breaks in tracks or shorts between tracks and pads. Repair if necessary. Check the hole sizes are correct for each component 62  Silicon Chip Taken at a low sweep speed, this waveform shows the transducer driven with bursts of different frequencies. In this case the maximum peak-peak voltage is 900V. Danger!! 1 FIRST WIND THE SECONDARY, USING 0.25mm ENAMELLED COPPER WIRE: TWO 45-TURN LAYERS, STARTING FROM PIN 4 AND ENDING AT PIN 3. PLACE ONE LAYER OF PLASTIC INSULATING TAPE OVER EACH LAYER. 6 45 TURNS 5 45 TURNS 4 S3 7 8 9 10 3 F3 11 2 12 1 13 ETD29 FORMER UNDERSIDE (PIN SIDE) VIEW 4 TURNS 2 THEN WIND THE PRIMARY, USING 14 x 0.20mm FIGURE-8 CABLE IN TWO LAYERS EACH OF 4 TURNS. TERMINATE THE START WIRES AT PINS 7 & 10 AND THE FINISH WIRES AT PINS 7 & 12. NOTE THE STRIPE WIRE TERMINATIONS. 6 4 TURNS S1, 7 F2 5 8 4 S3 9 S2 10 3 F3 11 2 F1 12 1 13 Fig.4: winding details for the on-board transformer, T1. The secondaries are conventional enamelled copper wire while the primaries are wound with figure-8 wire. to fit neatly. The screw terminal holes and transformer pin holes are 1.25mm in diameter compared to the 0.9mm holes for the ICs, resistors and diodes. Larger holes again are used for the DC socket and fuse clips. Normally, power can be switched on and off by switching the plugpack at the power point. However, if you prefer to have a separate switch for the Ultrasonic Cleaner, we have provided the option to include a power on and off switch (S2) that is wired between two PC stakes on the PC board. If you are not using the switch then the PC stakes do not need to be installed. If you are using a switch, then the PC stakes are installed and the thinned track between the PC stakes is broken using hobby knife. PC stakes are required to be installed for the three connection points for VR1. Assembly can begin by the inserting the resistors. When inserting the resistors, use the resistor colour code table to siliconchip.com.au help in reading the resistor values. A digital multimeter can also be used to measure each value. The diodes can now be installed, with the orientation as shown. Note that there are four different diode types: 1N5819’s for D1 and D2, 1N4004 for D3 and 1N4148’s for D4-D7. It’s probably safest to install D4-D7 first, being all the same type. IC1 is mounted on a DIP8 socket, with the notch positioned as shown. Install the socket now but leave IC1 out for the time being. The crystal (X1), the DC socket and the two 2-way screw terminals can be installed next, with the screw terminals oriented with the opening toward the outside edge of the PC board. Q1 and Q2 are mounted so that their metal tabs face the transformer and are about 25mm above the PC board. REG1 can also be mounted now. None of these components require heatsinks. The LEDs are mounted with the top of each LED 30mm above the PC board. Again, take care with orientation: the anode has the longer lead. Capacitors can be mounted next ensuring the electrolytic types are oriented correctly. The two main supply electrolytics (4700µF 16V) must be low ESR types. Winding the transformer Fig.4 shows the transformer winding details. The primary winding uses standard polarity-marked figure-8 wire, either 14 x 0.20mm or 14 x 0.18mm, wound in two layers. The secondary uses 0.25mm enamelled copper wire wound in two layers with a layer of insulation tape between the first and second layers. Start by winding the secondary winding. First, remove the enamel from the one end of the 0.25mm enamelled copper wire (use some fine emery paper or a hobby knife to scrape it off). Pre-tin the wire end and wrap it around pin 4 on the underside of the transformer bobbin and solder close to the bobbin. Now close-wind 45 turns (ie, side-by-side) until the windings reach the opposite end of the former. The direction of winding does not matter. Cover the windings in a layer of insulation tape. Continue winding back over the first layer, in the same direction as before (ie clockwise or anticlockwise) to complete 90 turns. Terminate the wire onto terminal 3 in the same way as was done for terminal 4. The primary winding, made from siliconchip.com.au Parts List – Ultrasonic Cleaner 1 PC board, 104 x 78mm, code 04208101 1 IP65 ABS box with clear lid, 115 x 90 x 55mm (Jaycar HB6246 or equivalent) 1 panel label 84 x 80mm 1 12V 2.5A plugpack 1 50W ultrasonic transducer with 40kHz resonance 1 65mm PVC DWV (Drain, Waste and Vent) end cap 1 65mm PVC pipe 40mm long to suit end cap 1 ETD29 transformer with 2 x 3C85 cores a 13-pin former and 2 retaining clips (T1) 1 2.5mm PC mount DC socket (CON1) 1 SPST momentary closed panel switch (S1) 1 SPDT toggle switch (S2) (optional) 1 3A M205 fuse (F1) 2 M205 fuse clips 2 2-way screw terminals (CON2, CON3) 1 DIP8 IC socket for IC1 1 knob to suit VR1 2 cables gland for 6mm cable 1 20MHz crystal (X1) 3 PC stakes (for VR1 terminals on PC board) 2 PC stakes (optional for S2) 2 solder lugs (Ultrasonic Transducer terminals) 2 M4 x 10mm screws (Ultrasonic Transducer solder lugs) 2 M4 nuts (Ultrasonic Transducer solder lugs) 2 4mm star washers (Ultrasonic Transducer solder lugs) 4 M3 x 6mm screws (PC board to case) 1m twin core mains flex (Ultrasonic Transducer lead) 1 300mm length of 14 x 0.20mm or 14 x 0.18mm fig-8 wire (primary T1) 1 3m length of 0.25mm enamelled copper wire (secondary T1) the figure-8 cable, is first stripped of insulation at about 10mm from the ends and the two wires are soldered close to the bobbin at pin 7 and pin 10. Place the wire with the polarity stripe to pin 7. Now wind on four turns making sure the wire lies flat without twisting so the striped wire stays to the left. The four turns should fully fill the 1 300mm length of black hookup wire (S1 and VR1) 1 50mm length of red hookup wire (VR1) 1 50mm length of blue hookup wire (VR1) 1 100mm length of yellow hookup wire (optional for S2) 1 240mm length of 2mm heatshrink tubing (VR1 and PC stakes and S1 terminals) 1 40mm length of 5mm heatshrink tubing (Ultrasonic transducer terminals) 1 40mm length of 5mm black heatshrink tubing (LED1,LED2 covering) Semiconductors 1 PIC12F675-I/P programmed with 0420810A (IC1) 1 78L05 5V regulator (REG1) 2 RFP30N06LE 30A 60V Logic level Mosfets (Q1,Q2) 2 1N4733 5.1V 1W zener diodes (ZD1,ZD2) 1 1N4004 1A diode (D3) 4 1N4148 switching diodes (D4-D7) 2 1N5819 1A Schottky diodes (D1,D2) 2 3mm LEDs (LED1,LED2) Capacitors 2 4700µF 16V low ESR 2 100µF 16V 1 10µF 16V 2 100nF MKT polyester 2 22pF ceramic Resistors (0.25W 1%) 1 22kΩ 1 10kΩ 2 2.2kΩ 1 100Ω 2 10Ω 1 10kΩ linear pot with knob (VR1) Miscellaneous Neutral cure silicone sealant suitable for wet areas (eg roof and gutter sealant) Epoxy resin (eg. J-B Weld) bobbin and the next four turns will be on the next layer (there’s no need for insulation tape between them). Terminate the striped wire end onto pin 12 and the other wire to pin 7. Once wound, slide the cores into the former and secure with the clips. These clips push on to the core ends and clip into lugs on the side of the bobbin. The transformer can be inA August ugust 2010  63 This scope waveform shows the cleaner in continuous mode whereby it is swept over a small range of frequencies centred around 40kHz. Taken at a low sweep speed, this shows that transducer drive is continuous rather than being pulsed at different frequencies. stalled into the PC board holes and soldered in place. Install T1 on the PC board noting that the primary side has seven pins and the secondary side has six pins. That completes the PC board assembly. overhead projector film, then mark out and drill the holes in the clear lid. The label is mounted inside the lid to protect it. Cut the holes out for the switch and potentiometer using a hobby knife, then attach it to the lid using clear tape, spray adhesive or clear silicone sealant. The switch and potentiometer are wired as shown using hookup wire and heatshrink tubing over the soldered terminations. The heatshrink tubing helps prevent the wires from breaking off the terminals. Note that the switch is best attached to the lid before connecting the wires to the PC board. The potentiometer can be wired while it is off the lid and attached after wiring. So that light only shines through the lid where the power and running indications are located on the front panel label, the two LEDs are fitted with short “light tubes”. We used approx. 20mm lengths of 5mm tubing and temporarily inserted the DC plug from the 12V plugpack into one end of the tubing to about 4mm inside the tube end. This acted as a heatshrink tubing former. Then the other end of the heatshrink tube was placed over the LED and the tubing was shrunk down using a heat gun. The DC plug was removed after the tubing had cooled leaving a round tube shape above the LED. Without the DC plug inserted first, the tube would shrink up too tightly. Holes are required in the ends of the box for the power connector and for the cable gland for the lead to the ultrasonic transducer. The power connector hole is 8mm in diameter and is located 31mm to the right of the outside left box edge and 16mm up from the outside base of the box. The 12mm cable gland hole is located on the opposite end of the box, 27mm up from the base edge and in the centre. The case Cut the potentiometer shaft so that it is 12mm long or to suit the knob used. The front-panel label shows the positioning for the start switch and the potentiometer that mount on the lid. This label can be downloaded from our website as a .PDF file. Print it out onto paper or clear Supply check Here’s how it goes together in the case. Only the timer pot (VR1) and the start switch (S1) are mounted on the lid of the case, which is translucent to allow the LEDs to shine through. 64  Silicon Chip The 12V 2.5A plugpack is supplied with several connectors. Choose the one that fits the DC socket, then attach this connector to the DC plugpack lead with the + marking on the connector plug to the + marking on the connector socket. With the plug removed from the DC socket, check that there is 12V at the connector plug and that the centre hole is the + terminal and the outside is the – terminal. siliconchip.com.au The transducer “potted” into some PVC plumbing fittings with silicone sealant, ready for attachment to a suitable cleaning tank. Make sure the terminals are covered! Now check that IC1 is OUT of its socket and remove fuse F1 (this step is important for safety reasons and to ensure F1 doesn’t blow with IC1 out of circuit). That done, plug the DC connector into the DC socket and check that there is 5V between pins 1 & 8 of IC1’s socket (pin 1 should be at +5V with respect to pin 8). In practice, this voltage could be between 4.85V and 5.15V but will typically be close to 5V. If the voltage is correct, switch off and place the board to one side. DO NOT install IC1 or the fuse – that comes later. Piezoelectric transducer Note that the voltage at CON3 and thus across the terminals of the piezoelectric transducer can be up to 900V peak-to-peak or so (see scope waveforms) – so avoid contact with these terminals when the driver is running. THIS VOLTAGE IS POTENTIALLY LETHAL! Use 2-core sheathed mains cord for wiring to the ultrasonic transducer. The wire terminates onto solder lugs and is covered with heat shrink tubing. The terminals are secured to the ultrasonic transducer terminals using an M4 screw, star washer and M4 nut for each. These terminals on the transducer are exposed and need to be protected within a housing to prevent contact. A suitable housing is made up using 65mm PVC DWV (Drain, Waste and Vent) fittings. As mentioned, the Ultrasonic transducer can be directly inserted into a bath if the transducer is raised sufficiently so that the lower 5mm of the transducer is immersed in the fluid. A typical housing is shown in the photo on page 58. Alternatively, the transducer can be secured to the outside RESISTOR COLOUR CODES No. 1   1 1   1 1   2 1   1 1   2 Value 22kΩ 10kΩ 2.2kΩ 100Ω 10Ω siliconchip.com.au 4-Band Code (1%) red red orange brown brown black orange brown red red red brown brown black brown brown brown black black brown Keeping the plumbing theme going(!), here’s our cleaning tank: an old cistern, with holes suitably plugged, with the smooth face of the transducer glued directly to the outside of the case using J-B Weld. You could use just about any metal or plastic leakproof container as a tank. Ours works a treat! of a “bath” using epoxy resin as shown above. We used an end cap and a 40mm length of pipe to house the transducer. The wire entry is via a cord grip grommet that secures to the end cap so that the wires cannot be pulled out to leave exposed live wires. Shape the cord grip grommet hole so that it is captured correctly within the end cap and holds the wire securely. The twin core sheathed cable we used was not held securely with the cord grip grommet and so we looped the cable in an ‘S’ shape so that three layers of the wire are captured in the grommet. The transducer should be mounted within the enclosure using neutral cure silicone sealant (such as roof and gutter sealant). The lower section of the transducer should be kept free from the sealant. This is so that the transducer can more effectively couple to the liquid in the bath either directly or when secured to the outside of the bath with epoxy resin. Make sure the electrical terminals are covered with silicone to provide insulation and prevent accidental contact. Connecting the ultrasonic driver cable to the PC board is best done before the board is mounted in the box. Ensure the power is off and pass the 2-core sheathed mains cord through the cable gland locking nut, the cable gland itself (which means it goes through the box) and carefully connect the two wires to the output terminals (CON3). Make absolutely sure there are no strands of copper wire emerging from the terminals which could short them out. The Ultrasonic Cleaner PC board 5-Band Code (1%) red red black red brown brown black black red brown red red black brown brown brown black black black brown brown black black gold brown Capacitor Codes Value µF Value IEC Code EIA Code 100nF 0.1µF 100n 104 22pF NA 22p 22 August 2010  65 can now be installed in the box and secured using the four M3 x 6mm screws. That done, pull the 2-core mains cable through the cable gland so it has a just little slack inside the box and secure the cable with the locking nut on the gland. Finally, complete the assembly by installing IC1 and the fuse (make sure the power is off), then fit the case lid. The bath When the Ultrasonic transducer is directly inserted into the bath, the bath can be made of almost any suitable material ranging from plastics through to glass and metal. For external attachment of the Ultrasonic transducer, the bath can be made from stainless steel, aluminium or plastic that couples the ultrasonic vibration through into the fluid. Thinner materials couple the ultrasonics with less loss. Ideally the bath should have a flat side or base where the transducer can be attached. The material also needs to be compatible with the epoxy resin used to glue the transducer to the bath. Metals are the most compatible material. Larger sized baths with more liquid will have a lesser cleaning effect than smaller containers with less fluid. A 200mm diameter or smaller cylindrical container or a similar sized rectangular bath size could be used with up to one litre of fluid in the bath. This is ideal for the ultrasonic sensor and driver. Alternatively a stainless steel kitchen sink can be pressed into service. The fluid used in the bath can be water with a few drops of detergent as a wetting agent. Other fluids that can be used include methylated spirits. Cleaning effectiveness is greatly enhanced when the fluid is warmed. Normal operation of the Ultrasonic Cleaner is where the frequency is cycled over the 19kHz to 42kHz range. Firstly, set the timer as shown on the front panel label for up to 10m. Pressing the start switch begins the cleaning cycle. The cleaning can be stopped at any time by rotating the timer potentiometer fully anticlockwise or switching off power. Power is indicated with an LED, while cleaning operation is shown with a second LED. The running operation will show the LED with a small amount of flickering. For stubborn hard to clean components, you can set the driver mode to the alternative setting. To do this switch off power and wait until the power LED is out. Then press the start switch and apply power. Hold the switch for a couple of seconds and then release the switch. This sets the alternative driver cycle that centres about 40kHz. Note that it is recommended that this alternative mode be only used intermittently and for less than a few minutes since the Mosfet and transformer run hot during this cycle. To return to the normal mode, firstly switch off power and wait again until the power LED is out. Then press the start switch and apply power. Hold the switch for a couple of seconds and then release the switch. This will return the cleaner to the normal driver cycle. So how can you identify which cycle is running? The setting when the Ultrasonic Cleaner is first built is the normal cycle. For this cycle, the running LED will flicker on and off and the transducer will emit its own distinctive audible sound. And yes the transducer is ultrasonic but some sound is heard as the transducer is swept over frequency. Sub harmonics and the frequency modulation are audible. For the alternative cycle, the running LED will be virtually flicker-free and the audible sound will differ SC from the normal cycle mode. Why is Ultrasonic Cleaning effective? A component that has contaminants on its outside layer can be cleaned by physical removal of the contaminants or by dissolving the contaminant. Which process works depends upon the contaminant. FIG.6 For example solids are more effectively removed by physical means whereas oils are better removed by dissolving in solution. Sometimes a combination of physical dislodging and chemical dissolving of contaminants is necessary to remove various combinations of contaminants. Ultrasonic energy improves both the dissolving and physical removal of the contaminant. Where ultrasonics is used as an aid in the dissolving process can be seen in the Figures from Fig.6 to Fig.8. Fig.6 shows a component that has a contaminant adhered to its surface that is placed in a cleaning fluid solution. As the cleaning fluid begins to dissolve the contaminant, it becomes saturated with the contaminant and so it loses its effectiveness in cleaning. This is seen in Fig.7. FIG.7 However, as shown in Fig.8, when ultrasonic excitation is included in the cleaning process, the saturated cleaning fluid is displaced allowing fresh cleaning fluid to come into contact with the contaminant to dissolve it. As shown, the component surface is a flat edge that could be cleaned with a mechanical method other than ultrasonics. For irregular and internal surfaces on a component, ultrasonics is very effective because it can reach where other mechanical removal means is impossible to gain access to the contaminated surfaces. Where the contaminant comprises solids that are not dissolved by the cleaning fluid, ultrasonics also aids in removing these particles from the component surface. However, the cleaning fluid must wet the particles so that this fluid can then carry the particle away FIG.8 from the component surface. The ultrasonics assists in the removal of the particle from the component and in the motion of the cleaning fluid as it carries the contaminant away from the component site. It is also possible that ultrasonics may increase the rate of chemical action in the dissolving of contaminants. 66  Silicon Chip CLEANING FLUID COMPONENT Fig.6 SURFACE CONTAMINANT CLEANING FLUID COMPONENT Fig.7 SATURATED CLEANING FLUID CLEANING FLUID CAVITATION BUBBLES COMPONENT Fig.8 SATURATED CLEANING FLUID siliconchip.com.au