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UER Forum > UE Encyclopedia > Inductive Probe (Viewed 3138 times)
Entry: Inductive Probe
originally posted by Zorb

[last edit 8/28/2008 12:33 AM by shotgun mario - edited 1 times]

A handheld telephone system (and less often electrical) service tool which detects electromagnetic fields and translates them into an audio signal. Example: Progressive Instruments (Also sold as Tempo, Textron) 200EP.

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In its intended use, a battery powered device (often called a "Toner") sends an audio signal through a length of wire, to be detected by the probe. This allows very rapid location of a single wire or pair of wires in a large bundle. It is also useful in its intended field to identify types of wires. Unfortunately, a good one can be quite sensitive, taking interference from AC wires, fluorescent light transformers, switching power supplies, and virtually anything else electrical other than a simple, non-modulated, DC lighting circuit driving an incandescent bulb or LED.

Our use for this tool is a little different. In a building, you cannot set the gain to its highest setting and activate the tool without hearing a multitude of sounds. You will hear 50/60Hz (AC), buzzes from fluorescent lights, hums from voltage regulated power supplies, and so on. Using this tool when investigating a building can be very useful, as various sensors produce distinct sounds.

- The alarm data bus line has an almost unmistakable harsh chopping sound.
- Alarm sensor wires have a high pitched, hollow sounding, switching power supply sound, as well as a slightly higher pitched clicking in many applications.
- Microwave sensors are electromagnetic hell, and sound as such.
- Fluorescent light transformers sound through the probe's speaker, just as the noisier ones do without any tools, you can just hear them farther away.
- AC power is low pitched hum or buzz, at around 60Hz. Three phase AC will be 180Hz.
- If you hold it up to an audio speaker line, you will hear the sound being transmitted, plus whatever interference you get off of the line transformers in some commercial installations.
- A sensitive probe will let you listen to a telephone conversation, though you may need an earphone, as the integrated speakers are rarely very good.
- Active Infrared hisses.
- Digital video feed from a security camera (90% of installations since 1999) sound like a lower frequency version of Ethernet.
- Serial data lines sound clipped and very very digital (harsh, on/off).

You get the point. This device will NEVER produce a false negative, as long as it's working for an AC line, unlike inductive/non-contact voltage testers, unless the voltage is too low to be meaningful.

Voltage * Current = Wattage = Amplitude (variable scale), Frequency = Frequency (1:1 correlation)

You can hear anything up to the upper limit of your hearing (20000Hz if your hearing is very good)
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