we are the manufacturers of conveyor saftey switches, viz travel end limit switches, pull chord switches, belt sway switches, etc.

These switches constitute a normally open contact or a normally closed contact which will be wired up in series to trip the motor.

there will be 200 switches in a length of a kilometer (approximately), we require a design Idea to know the status of a switch in a remote location.

 

You can use software-multipex.
For a maximum of 256 switches you wil need:
- one additional contact per switch
- one decoupling diode per switch
- 16 digital outputs
- 16 digital inputs

greetz
LargoD

 

Here is an idea for switches wired in series. In parallel with each switch place a circuit that draws very little current - so little current that when the switch is opened, the motor will not run. Inside this circuit place a microcontroller chip that will send short current pulses in a pattern that uniquely identifies that particular switch. These current pulses are too short to make any difference to the motor, but they can be detected at a central location, which can then make the information available in any manner that you choose.

I imagine that the most common situation is where only one switch is tripped, and that is the easiest one to get working. But with careful design, multiple switches could be accommodated too. The trick with multiple switches is to have each tripped circuit periodically short its input so that other tripped circuits can get sufficient voltage to do their signaling job. This can be done without any danger of powering up the tripped motor, and it does not require the running of any additional cable.

Robert Scott
Real-Time Specialties, Ypsilanti, Michigan
Embedded Systems Consulting

 

Responding to Sunil Cornelio's Nov 4, 11:29pm query... just some cautionary observations:

1) You haven't mentioned the country of installation, but if the US or Canada, are you sure the sanctioning authorities have accepted Energize-To-Trip (ETT) for safety-control circuits?

2) You haven't mentioned voltages used, but if AC, have you considered long-circuit wire-wire and wire-ground (earth) capacitance and how their
presence will influence system safety?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

thanks for the reply, can you be more precise,that will enable me to rig up a test/trial circuit.

sunil

 

Responding to the Data Communication part of Suni Cornelio's Nov 4, 11:29pm query:

In the late 50's I provided a design covering a similar situation, but for an offshore platform. The problem involved identifying which of many pushbuttons, located at every emergency-egress location, was actuated in a "Last-Off, Push" scenario. It was implemented using relays in a reiterative-contact design technique and an address header. It was somewhat smaller in the number of locations (about 40) and distance, about 200 ft.

In the '80's the system was upgraded using solid state data communication devices. In the late 90's it covered hundreds of points, and used fiber-optics (1 km) as the communication mode.... all without software.

If you are interested, I can put you in contact with a Company that can provide details. Contact me off- or on-list.

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])