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  • Field Strength Meter with Signal Connection Cables

Field Strength Meter with Signal Connection Cables
FSM+SCC

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Highlights

  • Cost effective simple solution for measuring, setting up and commissioning a hearing loop system to the requirements of IEC60118-4, updated in 2006.
  • Three modes of operations for three test types. A-weighted background noise, broad band mode (50 Hz - 8 kHz) and frequency response (100 Hz, 1 kHz, 5 kHz).
  • Includes the Signal Connection Cables

Overview

The field strength meter is a cost effective and simple solution for measuring, setting up and commissioning an hearing loop system to the requirements of IEC60118:2006 standard. The meter is an ergonomically designed hand held instrument for measuring loop system performance. There are three calibrated operational modes for the assessment of background noise, field strength and frequency response as required to ensure correct function of the loop system. The meter also doubles as a loop receiver with a headphone output to listen to the signal in the loop.

Includes

One (1) FSM Field Strength Meter
One (1) Stereo 3.5 mm to Dual RCA 6.6 ft. (2 m)
One (1) Stereo 3.5 mm to Balanced XLR and Electret Microphone Mono 3.5 mm
One (1) RCA to Mono ¼” Adapter
One (1) Audio CD with Test Signals
Two (2) AA Alkaline Batteries
One (1) Soft Carrying Pouch
One (1) Instruction Guide

Architectural Specs

The field strength meter shall measure the background noise by determining the level of background magnetic field present in the intended location for the loop system. It shall measure the field strength delivered by the system. The meter shall measure the performance of the frequency spectrum required by IEC60118:2006 standard. It shall have an audio output to allow to the signal to be heard through a headphone or earspeaker. The meter shall include a LED graph with a wide view angle that is color coded. It shall accept two (2) AA alkaline batteries and display an illuminated LED when the battery is at acceptable level. It shall include signal connection cables to allow testing with other devices. The FSM Field Strength Meter is specified.

Specifications

  Specifications FSM
Measurement Coil Orientation Vertical when held upright
Reference Level 400 mA/m (In field strength mode)
Frequency Response 50 Hz to 8 kHz ±0.25 dB, 30 Hz to 10 kHz -3 dB
Gain Stability Better then 0.5 dB over all conditions
     
Ouputs LED Bar Graph Color Coded - Green for -3 to +3 dB, Red for -4 to -22 dB
Audio 3.5 mm Stereo Conenctor, 16 Ohms (32 Ohms per side)
     
Power Battery Two (2) x AA Alkaline
Battery Monitor Battery OK when LED illuminated
Battery Life Up to 100 hrs. use, dependant on use pattern
     
Physical Size 3.3 x 1.0 x 5.5 in. (84 x 27 x 140 mm) (WxDxH)
Weight .33 lbs. (.15 kg)
Environment IP20 Protection, 20 to 90% Relative Humidity, 14 F (-10 C) to 113 F (45 C)
     
Specifications are subject to change without notification

None

Used With

Accessories

Support Documents

    • FAQ

    How do I choose which loop driver is best for my installation?
    Generally, this depends on the size of the room, the construction of the building, and the type of loop system you need. Refer to the Designing an Hearing Loop System Guide and Listen support to help you specify and design your system.
     
    When should I use a perimeter loop system and when do I need an array?
    A perimeter loop is the simplest form of loop system requiring a single loop of cable around the area to be used. However perimeter loops cannot be used if (1) other loop systems or areas where t-coil receivers are used are nearer than 3 times the room width (shortest side); (2) the room width is over 15ft and there is significant metal in the plane of the loop, such as reinforcement in a concrete floor. In these cases an array system is usually required. You may be able to conduct a site survey to confirm whether an array is necessary – contact Listen for details.
     
    What is an array system and how do I design one?
    An array uses two loop drivers and an SP5 phase shifter to create two overlaid magnetic fields, capable of accurately controlling the field within and around the loop system. They can be used to prevent ‘spill’ of magnetic field allowing loops to be used in adjacent rooms, and to give good even coverage in areas with metal building structures or complex installations. Arrays need a special layout design that can be provided by Listen. Arrays will always give a better field coverage and higher certainty of excellent performance than a perimeter loop, however the installation is more demanding and requires loop cables to cross the floor or ceiling of the area of use.
     
    What audio input should I use?
    Either an existing audio system can be used, or a dedicated microphone or other audio source may need to be provided. The objective is to ensure the loop system receives the required audio source (e.g. a voice) and not any background noise. The most essential job of any assistive listening system is to increase the level of the signal (the voice) relative to the background.
     
    Why is it important for a loop driver to be ‘constant current’?
    A current drive or constant current driver will deliver a current to the loop that is independent of the loop impedance. A normal audio amplifier will not be able to deliver constant current into a loop, meaning lower output at higher frequencies where the loop impedance is higher. A constant current driver can deliver flat frequency response, essential for delivering intelligible sound and performance that meets the loop performance standard.
     
    Which type of cable should I use?
    For cable intended to go under a carpet, you should use 1.8mm2 flat copper tape.  Otherwise, you should choose the cable based on the maximum total cable length in the specifications chart.
     
    What is spill or overspill?
    Overspill occurs when the magnetic field created by hearing loop can be heard outside of the looped area (such as a room).  The field is “spilling” outside of the looped area and can affect other nearby loop systems.
     
    How do you minimize overspill?
    This is done by using an array, consisting of two loop drivers and a SP5 phase shifter that controls the field within the looped area and reduces it rapidly outside the loop perimeter. The overspill can be reduced to as little as 5 ft (1.5m) with a good design.
     
    What is metal loss correction?
    Many buildings have embedded metal in the structure such as reinforcements in concrete, metal computer floors or suspended ceiling grids.  This metal causes a distortion of the frequency response if the metal is in the same plane as the loop cable.  The metal loss correction equalizes the audio to make up for or “correct” this loss. Note that metal loss will also reduce the signal level in general, and may require additional power, or indeed an array system to achieve the right level of performance.
     
    Why do loop drivers have extensive audio processing?
    Because the people who benefit from hearing loops (individuals with t-coil hearing aids), have limited dynamic range due to hearing loss.  Thus, these users require significantly reduced dynamic range so they can hear the softest of sounds and so that very loud sounds are brought to nominal level.
     
    Should I purchase a field strength meter?
    Absolutely, it’s the only way you’ll be able to determine if a loop system is operating properly. Any venue that owns and operates a loop system should also have some equipment to monitor the operation of the loop on a regular basis. This should either be a field strength meter (FSM) or a receiver with field strength indication (IR-IL-1).