Baldwin Boxall Communications Ltd.
Wealden Industrial Estate, Farningham Road
Crowborough, East Sussex, TN6 2JR
Telephone: 01892 664422 Fax: 01892 663146
Website: www.baldwinboxall.co.uk
Email: mail@baldwinboxall.co.uk
C O M M U N I C A T I O N S
IM10L
ECR1457
Issue 3 25/03/2003
M10L
Operating Instructions
- 2 -
Issue 3
M10L
The M10L is an audio frequency induction loop amplifier designed to drive loops at up to
10A-peak current. Whilst the amplifier may be used as a ‘stand alone’ unit it is normally
‘slaved’ from the main PA system, via the auxiliary input, the microphone input providing an
ambient noise input.
A tone control, accessible only from the underside of the amplifier, allows the installer to
adjust the frequency response of the amplifier to optimise the performance of the system.
An indication of the peak current flowing in the loop is provided by the bargraph display on
the front panel, along with limiter and protection indicators.
By selection of a slide switch (located on the rear of unit) a 1KHz test tone is enabled to
assist in the setting up of the loop output. The test tone may also be used to conduct periodic
testing of the loop installation.
Setting up Procedure
• Set all front panel controls to minimum (fully anti-clockwise) in order to gain maximum
benefit from the compression circuitry.
• Microphone and auxiliary input controls should be set such the that the limiting LED
on the front panel is just on when normal programme speech or music is applied (the
LED may flicker slightly)
• When the amplifier is connected to the loop the ‘loop current’ control can be adjusted
to provide the desired field strength within the loop which may be measured using a
field strength meter.
BS6083 Recommends field strength of 0.1 A/m long term average.
• In the absence of a convenient input signal, select the test tone on the rear panel to
the ‘on’ position to provide a constant 1KHz tone.
• Care should be taken when setting the loop current not to allow the protection circuitry
to operate (as indicated on the front panel LED). Should this occur, either the control
should be turned down slightly or a loop with higher impedance is required.
• When the field strength has been set, remember to return the test tone switch to the
‘OFF’ position.
Fuse Protection
3 fuses protect the amplifier and must be replaced with the correct type:
• Rear panel mains fuse 3.15A(T)
• Internal positive and negative DC fuses 6.3A(F)
- 3 -
Issue 3
M10L
Specification: Induction Loop Amplifier
AC supply 220/240V 50/60Hz IEC connector
Quiescent Power Consumption 12VA
Max. Power Consumption 300VA
Max. Current Into Loop 10Amps (Peak)
Frequency Response 100Hz to 5kHz
Loop Impedance 0.6 to 6.0 Ohms
Tone Control 8dB. Lift and cut at 5kHz
LED Indicators Bargraph indicating peak loop current
Limiter indication
Protection indication
Output Stage Protection Overload limited plus thermal protection (without Clipping)
Inputs Microphone 600uV, 600Ohms balanced
Auxiliary 80mV, 40KOhms
Fuse Protection Mains input fuse 1 x 3.15A (T)
DC fuses 2 x 6.3A (F)
Din Input Connections
Pin 1 Signal Input Pin 1 Not Applicable Pin 1 Signal Input
Pin 2 Screen Pin 2 Signal Ground Pin 2 Screen
Pin 3 Signal Input Pin 3 Not Applicable Pin 3 Signal Input
Pin 4 Not Applicable Pin 4 & 5 Link together
Pin 5 Signal Input Plug Only
Output Selection
The Loop output is provided
On the upper and lower pins
Of the output connector
Mitre Plug In Option
MIM16 – Auxiliary to balanced line converter card. By inserting this card onto the
connector inside the rear of the amplifier enables the operator to convert the unbalanced
auxiliary input into the balanced 80mV 20k Ohms line input.
LOOP
OUTPUT
1
2
3
4
5
Ohms Balanced
0.6mV at 600
Mic
Gnd
Signal n/c Sig
n/c
Gnd
Aux
80mV
Sig
47K n/c
1
2
3
4
5
1
2
3
4
5
Fitted With MIM Option
Balanced Signal
Input
Signal
Link
Aux Connections When
Gnd
- 4 -
Issue 3
Loop Current
(Volume)
Mains
Switch
Bargraph
Driver
Microphone Auxiliar
y
Mains
Socket
Mains
Input
Fuse
Loop
Output
Test Tone
Switch
Aux Input Mic Input
Tone control
Access
Front Panel View
Rear Panel View
010
5
010
5
010
5
microphone auxiliary loop current
M10L
protectionlimitingoutput current
2146810
C O M M U N I C A T I O N S
emi t r
VIEW OF MIM16 OPTION FITTED
BALDWIN BOXALL COMMUNICATIONS
LTD
ENGLAND TEL O1892 664422
UNDERSIDE OF
CHASSIS
TONE CONTROL
ACCESS ON
3.15A(T
)
DANGER! HIGH
VOLTAGE
E
N
L
LOOP
OUTPUT
DISCONNECT SUPPLY BEFORE ATTEMPTING
INTERNAL SERVICE
300VA
MAX
T
THIS
APPARATUS
MUST BE
EARTHED
WARNING !
220/240V
AC
50/60
H
Fitted With MIM
Oti
Balanced
Si l
Input
Signal
ON
OFF
TES T
TONE
4 2
3
Link
A
ux Connections
Wh
5 1
Gnd
Ohms
Bl d
0.6mV at
600
2
n/c 44 2 Sig
n/c
Gnd 33
Aux
80mV
Sig
47K n/c
5
Mic
5 1
EN
1364
1
2
Gnd
1
Signal
FUSE
PUS
H
1
2
3
4
5
1
2
3
4
5
2u High Rack Mounting Brackets Shown Fitted M2RACK
- 5 -
Issue 3
Induction Loop System Design
Having noted the approximate dimensions of the required induction loop the ‘Aspect Ratio’
may be determined. The aspect ratio is width (B) of the loop divided by the length (A) of the
loop. Using the graph below select the width (in meters) and move vertically to intersect the
appropriate aspect ratio line. From this point the correct wire size (cross sectional area) may
be selected. Always select the next wire size up from the intersection.
The peak current in the loop may also be determined by moving horizontally from this point
to the intersection with the vertical axis of the graph.
Example
Aspect Ratio = 12 = 0.6
20
Intersection from width B (12m) and aspect ratio line (0.6) occurs between the 0.22mm and
the 0.5mm cross sectional area would be selected.
The peak loop current may be read from the vertical axis as 6.6A
Care must be taken when designing and installing a loop system, particularly when
routing the cable. Avoid running the cable in or behind steel conduit or trunking. Also
avoid central heating pipes and running the cables along structural Steel work.
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10111213141516171819202122
0.22
0.5
0.75
1.0
1.5
1
0.8
0.6
0.4
0.2
0.1
WIDTH B (METRES)
PEAK LOOP CURRENT (AMPS)
A
S
P
E
C
T
R
A
TI
O
CABLE CROSS SECTIONAL AREAS (mm )
INDUCTION
LOOP
DIMENSIONS
Aspect Ratio = B
A
A
B
Induction Loop Amplifier
Current Graph
This graph is intended for your
guidance only. We will be happy to
advise on specific instalations.
2
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