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Alarm-Line detecting temperature increase (detection cable Alarmline LHD4 )
■ max. length: up to 300 m
■ able to detect temperature increase (at long distances) - resistant to mechanical and chemical impacts, corrosion, moisture, dust
■ easy to install, economical, easy to maintain, easy to commission
■ can be used in explosive areas
■ admission for operation VdS (No. g 295013), FM, CEGB
Alarm system Alarmline LHD 4 ensures timely detection of fire or overheating. It can be used in constrained rooms, under severe conditions, when other safety systems are not enough. The system consists of two elements: detection cable and signal forming unit Alarmline LHD 4.
Detection cable
Detection cable Alarmline consists of four copper wires. Each of the wires is enclosed into a jacket made of colorful insulating material with negative temperature coefficient, and covered by external heatproof coating. Metal braid is used to protect the detection cable if it is applied under severe conditions and under mechanical impact. The wires are connected as twisted pair isolated at the end of the cable. Both cable sleeves are controlled. Opening of the circuit and short circuit will result in emerency alarm activation in the signal forming unit. In case of temperature increase the electric resistance between both sleeves changes: resistance will be reduced. This change is detected by the signal forming unit, and when the set activation temperature is exceeded the alarm signal is made. If the temperature exceeds 100"Ñ and influences the detector for a short period of time, and after the signal is sent it restores its usual operation mode. If the detection cable is damaged the signal is sent constantly.
Signal forming unit
The signal forming unit informs about any temperature increase wi the help of the detection cable resistance control system. The activation temperature is set by means of a plug-type bonding strip which is installed in compliance with the gauge switch position. Two LEDs will illuminate/blink when there is alarm signal of damage. Both messages will block the signal forming unit. Reset will be done by interruption of power supply. The check key allows to carry out power electrical checkout of the system. The electric commutation system is located in a plastic box(polycarbonate: fire rating IP55). The unit is connected further to fire alarm systems with the help of volt-free contacts of the relay (2 À, 60 Â).
Temperature adjustment
The correct temperature is determined by nomogram taking into consideration two known factors: maximum ambient temperature in the controlled area. For example: 300 m long detection cable with maximum ambient temperature of 37,5 °Ñ. Length parameter of 300 m on D scale should be connected with the temperature paramenter of 37,5 °Ñ on  scale. The cross point will determine the set parameter 7 on À scale. And Ñ scale will determine the temperature for alarm signal both for the whole length and separate areas of the detection cable:
for 300 m length the signal will be sent at 49 °Ñ
for 30 m length the signal will be sent at 73 °Ñ
for 1 m length the signal will be sent at 114 °Ñ
Usage in explosive-risk areas
When installed in explosive areas the system should be provided with internal self-protection. In this case the signal formng unit should be installed in the area classified as risk-free, and commissioned Zenner barriers (2 barriers for each detection cable) will ensure installation of the detection cable in the area running less risk. Suitable barriers can be barriers manufactured by Measurement Technology under name MTL 761 ÀÑ.
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