Basic modules

4LSL. Loudspeaker Function Card

4LSL. Loudspeaker Function Card

At a Glance:

  • Active monitoring of impedance on 4 independent LF channels (configurable deviation thresholds from 1% to 99%)
  • Short circuit and wire break recognition
  • Ground connection message (recognition through TG01) and allocation of the loudspeaker circuit
  • Minimum load and overload monitoring (2.5 W>=load<= 150 W)
  • Distribution of loudspeaker circuits through independent power relays
  • Generation of positive or negative public address ac-knowledgements

In order to make a public address announcement it is necessary that the loud-speaker circuits to be used are in functioning order. One way to gauge this is to use the impedance which was measured during commissioning.

The 4LSL can be used to cyclically check loudspeaker circuits for deviations in impedance.

To do this a measurement signal is required which is generated by the TG01 module. The functionality of the signal generator is also tested before each measurement cycle by the 4LSL.

Brief Drscritption:

The 4LSL is part of an application for monitoring impedance in loudspeaker cir-cuits and distributed loudspeaker circuits. It switches the sine wave generated by the test signal generator to the loudspeaker circuit and compares the flow of current and the voltage with previously made reference values.

Fig. Application example of loudspeaker circuit monitoring
Fig. Application example of loudspeaker circuit monitoring

The principle functions are illustrated in the following block diagram.

Fig. Block diagram 4LSL
Fig. Block diagram 4LSL

The 4LSL consists essentially of a control unit, a measuring circuit and 4 inde-pendent sets. Each set has a low frequency (LF) input (usually from the V100 amplifier) and a loudspeaker output.

Required for the impedance measurement is the measurement signal generated by the TG01. Locking by the relay ensures that only one action can be carried out on the set, and that the LF signal does not reach the TG01. The measurement signal (125 Hz) is given on the loudspeaker circuit. The current flowing there is added to the measurement circuit through an input transformer and analysed to-gether with the output voltage. All processes are controlled through configurable programmes in the ICS software.

For a public address system the LF signal is added to the loudspeaker circuit through an output transformer.

Displays and messages are regulated by the control unit.

Public address and testing in a loudspeaker circuit are blocked off from one an-other. Public address has higher priority; a test is carried out after a public ad-dress.

Function Description:

The following functions are available on the 4LSL:

Monitoring of Impedance

New installations or changes in a loudspeaker circuit are monitored for changes in impedance behaviour with the help of the 4LSL module.

For this the installed and manually tested loudspeaker circuit is measured with the 4LSL module and its impedance is determined. The reference signal (125 Hz audio signal) required for this is generated and made available by a differ-ent module (TG01).

Schematic illustration of impedance monitoring
Fig. Schematic illustration of impedance monitoring

Measurement of the connected loudspeaker circuit is automatic. For this the au-dio signal generator is tested for proper functionality as well as the loudspeaker circuit for falling short of the minimum loudspeaker load and exceeding of the maximum loudspeaker load (load >= 2.5 W or <= 150 W). If the audio signal generator is not working properly (audio signal monitoring), or if the load of the connected loudspeakers is outside the indicated limits then this is indicated by the LED and system messages. Re-measuring is then automatically prevented. Re-measuring only becomes possible with a proper basic measurement.

Short Circuit and Wire-Break Recognition

In loudspeaker circuits wire breaks and short circuits occur that are caused by external effects and which lead to the outage of the loudspeakers. Short cir-cuits or wire breaks are detected and signalled by the 4LSL module during each subsequent measurement of the loudspeaker circuit.

When the service technician does the commissioning of the measuring module, the function “Loudspeaker Circuit Safety Switch-off” [LK- Sicherheitsab-schaltung] can be activated. If a short circuit has been detected then it results in a safety switch-off of the loudspeaker circuit. It switches off the loudspeaker circuit that has the short circuit and prevents it from being turned on again. The safety switch-off is only withdrawn after a subsequent measurement is made without a short circuit in the loudspeaker circuit.

Generation of a Public Address Acknowledgement

When public address announcements are made to remote locations it cannot be checked in person whether the announcement functioned properly or not. For this the 4LSL measuring module generates a positive acknowledgement when a public address announcement functioned properly.

To do this the 4LSL measures the power output (current and voltage) on the loudspeaker circuit and compares it with configurable reference values.

Sufficiently high power consumption and the associated acoustic pressure re-sults in a positive “public address acknowledgement”.

A positive public address acknowledgement is only given when a loud-speaker circuit has a minimum amount of capability to make a public ad-dress.

To check this the LED on the front plate can be switched to display mode “VU Meter”. Here the precise measurement level is displayed for each public ad-dress measurement and each impedance measurement. Each channel (set) can be switched over.

If a negative public address acknowledgement is additionally desired then this can also be generated by the 4LSL measuring module.

Earth Leakage Message

If earth leakage is detected on the TG01 (audio signal generator) then this is al-located unambiguously to a loudspeaker circuit by the 4LSL measuring module, the message “Earth Leakage” [Erdschluss] is displayed and the passed on to the DVS-21 system.

Commissioning Functions

The 4LSL measuring module includes additional commissioning and servicing aids to better control the measurement equipment or the loudspeaker circuits.

These are:

  • Switchable drive display (VU meter) to check precisely all signals to be measured
  • Display of the most important functions on the front plate
  • Automatic or manual calibration of loudspeaker circuits
  • Diverse group and individual messages
  • PC-based configuration
  • Measurement data transmission to the DVS-21 central system
  • Simulation of all processes which the module has

Summary of the Functions

  • Precision measuring for impedance error detection: 1-100% in 1% steps (% of installed loudspeaker load)
  • Number of independent loudspeaker circuits or measurement channels: 4
  • Measurement channels can be individually switched on/off
  • Loudspeaker minimum/maximum load per channel: 2.5 Watt / 150 Watt
  • Loudspeaker load check during commissioning
  • Manually or automatically configurable impedance deviation limits
  • Verification of impedance deviation through automatic multiple subsequent measurements
  • Automatic or manual measuring procedure
  • Checking of the test signal generator before each measurement
  • Wire breakage or short circuit detection
  • Allocation of an occurring earth leakage to a loudspeaker circuit (earth leak-age detection through TG01)
  • Transfer of all measurement data to the DVS-21 central system
  • Display of all statuses by LEDs on the front plate
  • Loudspeaker circuit relays: 4 (1/channel)
  • Generation of positive and negative public address acknowledgements
  • Programmable night-reduction function for public address acknowledgement
  • Configurable amplifier protection function for loudspeaker circuit short circuit
  • Making possible public address in the case of a short circuit (group public address)
  • Diverse group and individual messages
  • Full control over all procedures through the DVS-21 central system
  • PC-based configuration
  • Commissioning and service aids on-board

Further details can be found in the commissioning instructions.

The Front Plate Symbols and Their Meaning:

The system blinker The system blinker
Addressing from processor taking place
I/O Input/Output
BUS output works as push-push operation with the system blinker
BUS input works as push-pull operation with the system blinker
M Status Display for Impedance Measurement, and Display of Level(depending on set)
impedance measurement active/ inactive/ interrupted
On Display of Status for Public Address, and Display of Level (depending on set)
Error Notification LED and Display of Level (depending on set)

Technical Data:

Operating Power (48V): max. 36 mA
Operating Power (+5V): max. 38 mA
Temperature Range: 0 °C to 45 °C
Weight: 300 g
Installation Height: 3HE
Installation Width: 6TE