Stopping low volume sounds when piezo alarm should be off?

Passives Audio Products
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A question that comes through the technical department on occasion is concerning a low volume noise coming out of a customer’s piezo alarm when the alarm should be off. Because many of these alarms are designed to operate with very little current they can make faint sounds with very little voltage. Due to this there are times these alarms can make noise with a small amount of leakage voltage in the system.

When speaking with my product manager for our line of Mallory Sonalert Products he offered me 3 possible solutions to this resolve the issue of leakage voltage causing the noise.

  1. Put a 30 V Zener transient voltage suppressor diode in series with the alarm such as P6KE33A or P6KE36A.

  2. Another option would be to parallel a 12-20 watt resistor across the alarm’s terminals. For 120 VAC applications a 2,000 ohm resistor such as Ohmite P/N B20J2K0 would be suggested. For applications using 250VAC try a 5,000 ohm resistor such as B20J5K0. Using lower Voltage you can look at a 1,000 ohm resistor such as B20J1K0.

  • A note should be made when placing the resistor in the circuit as to not touch any heat sensitive components including the housing.
  1. You could also choose to parallel an incandescent bulb just like the resistor across the terminal. You would need to match the bulb to voltage and watt rating appropriately.
  • Note that when the alarm is activated the full supply voltage will be seen at the lamp causing it to brighten.

Mallory has an entire list of FAQs available on their 22mm Industrial Alarms available below.
FAQ-22mm Industrial Alarms with Terminal Block.pdf (278.3 KB)

Applicable Part Numbers

ZA120MACT ZA120LACT ZA120LAFP1 ZA120LASU2 ZA120LADT7 ZA120SAFP1 ZA120MAFP1 ZA120MAMP1 ZA120MASP1 ZA120SAMP1 ZA120SASP1 ZA120SADP2 ZA120MADL1 ZA120MAPS1 ZA120MASS1 ZA120MASU2 ZA120SADL1 ZA120MADP2 ZA120MADP3 ZA120SADP3 ZA120SAPS1 ZA120SASS1 ZA120SASU2 ZA120LAMP1 ZA120LASP1 ZA120LADL1 ZA120LAPS1 ZA120LASS1 ZA120LADP2 ZA120LADP3 ZA120MACM1 ZA120MASR8 ZA120MASR9 ZA120SADT7 ZA120SADT8 ZA120SASR8 ZA120SASR9 ZA120MADT7 ZA120MADT8 ZA120SACM1 ZA120LASR8 ZA120LASR9 ZA120LADT8 ZA120LACM1