Table of Contents
General Alarm Technology
An electronic audible alarm produces an audible warning sound using electronic means. This is in contrast to electro-mechanical alarms that produce sound by mechanical means. Examples of electro-mechanical alarms include the old clapper-type alarm clocks, school bells, and car horns. Examples of applications that use electronic audible alarms include smoke detectors and microwave ovens.
Buzzers, beepers, audible signals, piezo’s, sounders, alerts, audio alarms, indicators, transducers, and various combinations of these terms (audio alerts, piezo indicators, etc.).
Audible alarms work by using electronic components to convert the user’s input voltage into an appropriate oscillating signal that drives a metal sounder diaphragm. This metal sounder diaphragm then physically flexes up and down producing air pressure waves that the human ear interprets as sound. For a more detailed description, please read the Article titled, “Audible Alarm Basics” and see Technical Application Guide, "Piezoelectric Alarm Operation".
Piezoelectric type alarms utilize a piezoelectric transducer which consists of a metal disc that has a ceramic material bonded to it. When voltage is applied to the ceramic material, it causes the metal disc to physically flex. If the piezoelectric transducer is physically flexed at an appropriate frequency, the air pressure waves are produced that are heard as an audible sound.
Electro-magnetic type alarms utilize an electro-magnet and a nearby bare metal disc that is mounted to the housing. When the electro-magnet is energized, the resulting magnetic field physically deflects the bare metal disc. If the bare metal disc is flexed at an appropriate frequency, an audible sound is produced.
Alarms that use piezoelectric technology draw less current, are capable of louder sound levels, and do not generate magnetic fields (possible EMI/EMC concerns). Alarms that use electro-magnetic technology excel at producing low frequency pitch sounds in small packages. This is why many miniature board mount or surface mount audible alarms use electro-magnetic technology.
Electronic audible alarms are considered components by equipment designers, but in actuality, they are a complex electromechanical assembly. See Technical Application Guide, "Piezoelectric Alarm Construction".
In order to solder wires to a stainless steel metal diaphragm, very hot temperatures and aggressive acid fluxes are required. The process is very sensitive to many different parameters, so if the soldering process slips out of control, weak solder joints can result. The soldering process needed to solder to a brass transducer does not need aggressive fluxes and extra hot temperatures, so the process is more reliable. In addition, the brass metal diaphragms are lower in cost, so the customer gets more value for their money whereas the stainless steel diaphragms are higher cost with no value added to the user.
The claim that stainless steel diaphragms are more corrosion resistant is false. In only the most severe salt water applications will a slight difference in the corrosion resistance be noticed. For these rare severe salt water applications, a conformal coating can be applied to the exposed brass surface (at a cost still less than stainless steel) that will provide equal or better corrosion resistance than the exposed stainless steel surface.
An indicator is an electronic alarm that has internal circuitry. The user only needs to apply an input voltage, and the alarm will automatically sound.
A transducer does not contain any internal circuitry. The user has to supply the complex AC signal that will make the sounder diaphragm flex at the appropriate rate and amplitude.
Indicators are always appropriate to use. Mallory’s design engineering (which holds over a dozen active patents) has already designed the most efficient circuit needed to produce the required sound and has tested that circuit against a wide variety of environmental conditions.
Transducers may be justified to use when there is sufficient volume to the application to justify the time and expense required to design, de-bug, test, re-design, and validate the circuit design needed to drive the transducer under the environmental extremes that will be seen in the application. While the operation of the transducer may seem simple from the outside, there are many potential application problems that can arise unexpectedly.
Electrical Application Issues
You are experiencing a leakage voltage with your power supply or controller. Mallory alarms are designed to operate with very little current, and it takes only a small amount of voltage to make the
alarm sound. Three possible fixes:
- Put a 30 Volt zener transient voltage suppressor diode in series with the Sonalert alarm such as ON Semiconductor P/N's: P6KE33AG or P6KE36AG or P6KE30AG. These should be readily available at many electronic distributors. You can also use: www.eem.com to find distributors who have these in stock.
- Parallel a 12 to 20 watt wire-wound resistor across the alarm’s terminals. For 120 Vac, try a 2,000 ohm resistor such as Ohmite P/N B20J2K0. For 250 Vac, try a 5,000 ohm resistor such as Ohmite P/N B20J5k0. If these resistor values do not solve the problem, or if you are experiencing the problem with a lower AC or DC voltage, then try a 1,000 ohm resistor. Make sure that the resistor is not touching the alarm housing or other components that may be affected by the heat being dissipated by the resistor.
- Parallel an incandescent (tungsten filament) pilot light across the alarm terminals. For 120 Vac, use a 6 or 7 watt bulb. For 250 Vac, use a 10 watt bulb. Possible sources:
McMaster-Carr: P/N 1628k34 (120 Vac; 6 watt incandescent lamp)
McMaster-Carr: P/N 8358k11 (250 Vac; 10 watt incandescent lamp)
Sylvania P/N 13609 (120 Vac; 7 watt incandescent lamp)
Sylvania P/N 16938 (120 Vac; 6 watt incandescent lamp)
Sylvania P/N 16717 (250 Vac; 10 watt incandescent lamp)
Remember that when the alarm is activated, the full supply voltage will be seen at the lamp causing it to brighten.
Yes. Mallory Sonalert AC/DC alarms work with both 50 Hz and 60 Hz systems.
There are two ways to adjust the volume level.
One way is to use our SCVC accessory which enables the user to manually baffle down the volume of the alarm. Fully closed, the SCVC will cause a 10 to 15 dB attenuation of the sound level (about ½ as loud as before).
The second way is to change the voltage going to the alarm. The sound level of the alarm is directly related to the voltage applied across the sounder element. For a fixed supply voltage, you can use resistors or a potentiometer (analog or digital) to adjust the voltage being applied to the alarm. It does take a fairly wide voltage swing to get a significant change in sound level, so there will be little sound level change with electromagnetic type buzzers because their voltage ranges are already too small to begin with. See Technical Application Guides, "Controlling Sound Level Mechanically" & "Controlling Sound Level Electronically".
A piezoelectric or electromagnetic alarm generates sound by physically deflecting a metal disc. It does take a small amount of time once the voltage signal is applied to the part before the metal disc is flexing to its fullest potential. Our recommended minimum pulse duration is 50 msec. but some customers have reported being able to use even shorter durations without affecting the sound level. At some point as the pulse duration continues to decrease, the "beep" sound will become a "click" sound and the sound level will decrease.
You can use a simple zener diode & transistor circuit. See Technical Application Guide, "Circuit to Increase Turn-On Voltage".
The input impedance of a piezoelectric transducer looks like pure capacitance. The current and voltage waveforms across the transducer can be predicted from the source voltage impedance and the transducer capacitance.
For Mallory Sonalert piezoelectric transducer type alarms, the sound level curves are generated with a square-wave with a 50-Ohm source impedance. You can increase the source impedance to a few hundred Ohms with negligible effect on the resulting sound output.
For Mallory Alarms and buzzers that use piezoelectric transducers, we have never had a report of these devices being affected by EMC/EMI. However, there have been a few reports of electromagnetic type buzzers being effected. If you are worried about the alarm being affected by EMC/EMI, you can consider using an EMC protective product such as 3M EMC tape or fabric that could be wrapped around the alarm. Google "3M EMC Products" to find 3M's website with information on these products.
Mechanical Application Issues
Here are the recommended hole sizes:
- SCE/SC/LSC/VSB Series: 1.25” (these series will fit through a 30mm hole).
- ZA 22mm Series: 22.5mm (0.896") with keyway.
- SNP Series: 1.063”
- Tamperproof Series (PK-27N35ER, PK-27A35EP, etc.): 33-34mm (1.30-1.35”)
- 22mm With Wires Series (PK-20A35EW, PF-20A35EW, etc.): 20mm (0.80”)
The standard termination for our SC & LSC series is screw terminals using #6-32 screws. You can ignore the screws and solder directly to the terminal. You can strip your wire and simply wrap it around the screws. A more popular choice is to crimp a spade or ring terminal to your wires to connect to the screw terminal. The terminals are also suitable for use with ¼” disconnect female terminal that have a 3/16” opening. One source for a female quick disconnect terminal is:
For our SNP Series, you can solder to the part’s terminals or use a 1/8” quick disconnect terminal.
For the plastic knurled nut, a maximum of 10 in-lbs is recommended. If your panel is not very thick, then it is likely that the nut will not strip until 20+ in-lbs is reached. For the metal knurled nuts, a maximum of 20 in-lbs is recommended.
For the SC/LSC/VSB series, the recommended torque is 4 to 6 in-lbs, and the maximum torque is 8 to 10 in-lbs.
As the picture to the left shows, the locking flats are only located at the base of the nose ring. The locking flats do not extend up the side of the nose threads.
For a vast majority of applications, the locking flats do not need to be used. If the knurled nut (not shown) is properly tightened, the alarm will not move in the application. However, for some high end applications with a lot of vibration (such as aerospace), the locking flats would help to ensure that the alarm will not rotate within the panel which could end up putting pressure on the wiring connections to the terminals of the alarm.
Yes, but the alarm will be attenuated 15-20 decibels. This means that the sound level will be about ½ to ¼ as loud as it would be if it was mounted externally or if there were openings made in the enclosure so that the sound could radiate out. For a full discussion on mounting alarms inside of equipment, read the article titled, “Audible Alarm Use and Equipment Integrity Issues.”
Yes! Visit our contact page on the website or email firstname.lastname@example.org or call 317-612-1000
Soldering & Washing Issues
330°C for 1.5 seconds or 270°C for 4 seconds.