Relay Usage? 1

[bigmil]

Hello,
I am a Mechanical Engineer and I am alittle lost here. This should be simple. We are try to hook up a automatic kill switch, so that when one piece of equipment goes down the other will shut down aswell. With the 1st machine we have a signal coming out that is .75V when it is on and 0V when it is off. The 2nd machine we have two terminals that when touched together will shut that machine off properly. I was thinking just hook up a relay to the .75V so when it goes off the relay connects the two terminals. Now I don't even know if that would work, but if it would, I am having a hard time finding a relay that would work? Is this possible? And if so where do I look for a relay? A coworker had mentioned something about a transistor, but from what I can remember, that wouldn't switch the power off?
Thankyou for the help,
Bigmil

 

[melone]

1) You can use a transistor to generate the coil current for a normally-closed relay. (using a relay keeps the two teminals isolated - nice and safe) It would be nice if you could define the output signal from the first machine, and the input requirements for the seconde machine, i.e. current, voltage, etc.. One drawback with using a relay is that a relay is mechanical in nature. This means that it can wear depending on the usage. If your machine cycle the power frequently, then you can wear out the relays and cause unwanted effects.

2) There are many places to find relays: Allied Electronics, Newark Electronics, McMaster-Carr... However, before you start looking for relays, let's make sure that we know all the system requirements first.

Keep us posted!

 

[bigmil]

I am not exactly sure what you mean by define the output signal but here goes: DC, Voltage on is .75V, Voltage off is 0V, Current on is 1.1MicroAmps. The input requirments for the second machine is nothing, what I mean is, all I have to do is connect two terminals together on the back of the machine and it goes through its shutdown. So I don't need to put any power in. I just need to connect these terminals. As far as I know that is all of the information on the system.
Just in case here are a few more details: Machine 1 is a oil fired burner, machine two is a computer controled electrodynamic shaker. When the burner faults out it automatically shuts off, we want our shaker to shutdown when the burner faults out. The terminals for the shaker are on the back of the computer and the terminals for the burner come out from a control box.

Thankyou,
Bigmil

 

[melone]

1) What I was looking for is how much current is going to flow when we connect the 2 terminals together? I would hate to recommend a small relay and find out that we need to pass 10A's throught the device. However, since you stated that the terminals were coming out of the back of a computer, the current requirements are probably fairly small, less than 1 Amp.

2) When machine 1 "turns off", does it kill the power? I am just wondering whether the machine goes into a standy mode and drives the output to a logic 0 state, or does the logic no longer have any power and floats down to 0V. This makes a big difference in whether the simple transistor solution will work. If the machine is driven low, then we can connect the base of a PNP transistor (via a resistor) to the output terminal of the first machine. This transistor will act like a switch and determine whether the normally-closed relay is activated. However, if the output (machine #1) floats low, we can no longer use a simple transistor switch to control the relay.

3) What DC voltage sources to you have available on either machine? What is their current capablities?

4) Is space a consideration?

5) How often do these machines cycle power?

Hope this helps!

 

[MMAshwin]

Hi,

You might just want to try a Normally Closed relay (NC) which is energized from an external power source and switched on by a transistor. The transistor is conducting because of the 0.75v on the base/gate.

Or

Use an opto isolator power mosfet type of arrangement.
However this relaies on knowing if the computer based equipment has voltages between the two terminals (which get shorted out) when the machine is on and the contacts are not connected together.

Let me know if you want me to draw you a schematic diagram.
Email at tps72v4@hotmail.com

Regards