Listen Technologies TFSM01 – IEC 60118-4 Field Strength Meter

Product Overview

The Listen Technologies TFSM01 is a magnetic field strength meter for commissioning and certifying hearing loop installations to IEC 60118-4. A hearing loop cannot be signed off by listening to it; the standard is expressed in field strength, background noise and frequency response, and all three have to be measured. This is the instrument that produces those numbers. Any integrator installing hearing loops needs one, because an accessibility consultant will ask for the measurements rather than an assurance.

Product Description

Three measurements determine whether an installed loop meets IEC 60118-4, and the FSM covers all three.

Field strength is measured broadband from 50Hz to 8kHz on a -22 to +8dB scale, with true RMS detection calibrated so that 400mA/m reads 0dB — the reference the standard is written around. Background noise is measured A-weighted from -42 to -12dB, which is what catches an installation compromised by dimmer buzz or switch-mode noise rather than by the loop design. Frequency response is checked in third octave bands at 100Hz, 1kHz and 5kHz, which is where metal loss in the structure shows up.

The display is a flying spot LED bar graph with a wide viewing angle, colour coded green between -3dB and +3dB. That matters when you are holding the meter at head height in the middle of a room and reading it at an angle. A 3.5mm stereo output with volume control lets you listen to what is being measured, which is how you identify an interference source rather than just recording that one exists.

Meter accuracy is 50Hz to 8kHz ±0.25dB, extending to 30Hz-10kHz at -3dB. It runs from two AA alkaline cells for up to 100 hours, weighs 150g and measures 84 x 27 x 140mm, so it lives in a toolbag rather than a flight case. It ships with a soft carry case, operating instructions, a commissioning guide template and test signal downloads.

Signal connection cables are ordered separately as the ACSCC cable set, or specify the TFSM01SCC bundle to get meter and cables together. Where the building structure contains significant steel, a metal loss test driver is used at survey stage to quantify the loss before the loop driver is selected.

Key Features

• Three IEC 60118-4 measurements — Covers field strength, background noise and frequency response, the three the standard requires.
• True RMS detection — Calibrated so 400mA/m reads 0dB, the reference the standard is written around.
• Colour coded LED bar graph — Reads clearly at arm's length and at an angle, with green marking the -3dB to +3dB target band.
• Third octave response check — Measures at 100Hz, 1kHz and 5kHz, where metal loss in the structure becomes visible.
• A-weighted background noise mode — Identifies installations compromised by dimmer or switch-mode interference rather than loop design.
• Audio monitoring output — Lets the engineer hear the interference source rather than only record that one exists.
• 100 hour battery life — Runs from two AA cells, so commissioning is not dependent on charge state.
• Toolbag sized — 84 x 27 x 140mm at 150g, with a soft carry case included.

Typical Applications

• Auditorium
• House of worship
• Government space
• Conference room
• Training room
• Multi-purpose room
• Commercial meeting space

Technical Specifications

Specifications sourced from the Ampetronic FSM field strength meter datasheet (UP34302-12).

Frequently Asked Questions

Why can't a hearing loop be signed off by listening to it?
IEC 60118-4 is expressed in measurable quantities: field strength relative to 400mA/m, background noise, and frequency response across the speech band. A subjective listening check demonstrates none of those and will not satisfy an accessibility consultant or building control.

What does the meter measure?
Field strength broadband from 50Hz to 8kHz, background noise A-weighted, and frequency response in third octave bands at 100Hz, 1kHz and 5kHz.

Do I need the cable set as well?
Yes, for measurements taken at the driver. The ACSCC cable set is ordered separately, or specify the TFSM01SCC bundle to get both together.

How do I survey a building with a steel structure?
Metal absorbs magnetic field strength, so the loss has to be quantified before the driver current rating is fixed. A metal loss test driver is used for that at survey stage; the field strength meter then verifies the finished installation.

What is supplied with the meter?
A soft carry case, operating instructions, a commissioning guide template, batteries, and access to test signal downloads.

How long does the battery last?
Up to 100 hours from two AA alkaline cells, which are supplied.

What warranty and support apply?
Warranty duration and technical support terms are set by Listen Technologies. Contact Creation Networks for current terms and for guidance on hearing loop commissioning procedure.