Normal practice today is to annunciate switches with double throw contacts, one for shutdown and one for annunciation in the PLC such as the frequency shift key type. THere are variations of this for above and below ground use.

There are light annuciations and flag annunciations which rotate into the field of view on activation with many variations. ■

Hello Rekhawa

Here in South Africa we use two types of pull cord system:

- Intelligent which we use for long systems

- Unintelligent which we use for short systems.

The unintelligent ones are cheap simple ones with the flag which pops out of the trip switch that has been pulled, as you describe.

The intelligent ones have a flag as well as a red light on the trip switch if it has been pulled, as well as a display unit in the MCC room that tells you if indeed it was a trip switch or a mis-alignment switch or belt rip or whatever, which one where and when.

This information is also relayed to the control room.

A supplier of intelligent systems here is CT Systems

Regards

LSL Tekpro ■

Dear Mr. Rekhawar,

Resently, I used LED type indicating lamp for indentification purpose in TATA STEEL. The Indian supplier are as below;

1. JAYASHREE, PUNE

2.JAYBALAJI, VILLAI

3.TECHNO CRAFT,KOLKATA

But I am not satisfied with the performance.

Regards.

A.Banerjee ■

Dear sir

long distance conveyor we devide total conveyor length in to small zones consisting of about 500 m length each .

Each zone will be having swiches at a distance of 50 m. Switches of each zone will have seperate circuit.

In case any pull chord switch is operated zone no of that perticular switch is annunciated at plc panel.

In field we have red lamp provided on each zone . in addition each pull chord switch have red lamp.

in case of particular pull chord switch is operated red lamp in the field of that zone along with lamp of swich will be operted.

This way it is very easy to locate operated pull chord switch

A R SINGH ■