Security Electronics Circuits Manual

6

Instrumentation security circuits

In its simplest form, an instrumentation security circuit is one that activates some kind of electromechanical slave device (such as a relay or solenoid) or alarm unit (such as a siren and/or light strobe) when a monitored voltage, current or resistance value goes above or below some pre-set limit. In practice, this monitored voltage, current or resistance may actually be derived from the output of a transducer that monitors a parameter such as motor speed, liquid flow rate or pressure, or rate of linear movement, etc., and such circuits thus have many practical applications in commerce and in industry. This chapter presents a selection of basic but useful security circuits that can be used to monitor ac or ...