Where industrial type "conductive sensor"??

[Tofo]

Dear all,

I am not sure whether I use the correct term. What I want is to detect whether a metal strip (5" long) sits on both point A and point B. I need a little voltage on point A. If the metal strip sits on both point A and B, then this system becomes a close loop.

Since I am designing a machine for medical product, I don't want any mickey mouse stuff in my design. Any industrial sensor available for that?

Thanks

 

[Gil47]

Some of the description you give can be achieved by doing a google search for
" floatless level controller omron "

Now the catch is if this is for medical use with a patient it will never get approval

I suspect you would be better served by using a magnetic reed switch or an inductive prox or a photo electric prox all are encapsulated devices which should get approval

 

[mendonsy]

SSAC makes a similar product called an LLC4 which works by sensing resistance to ground. The problem might be that the open circuit voltage is about 12 volts.

 

[keithkyll]

Honeywell medical sensors. If you want low current, look for Intrinsically safe switches.

 

[Tofo]

Thanks for the replies. I think I did not explain well. Technically, I need an industrial method of implement "Short circuit detection function of a multimeter" into my machine. The metal strip will be used to complete the loop. Instead of the buzz from the multimeter, I will send the signal to a PLC. Please help

The machine will make medical product, but the machine will not directly use on patients (You can think about I am design a machine to make resistors for a spaceship). My main concern is the safety of the operator who makes the part using my machine. I know that low voltage would not get hurt, but I need an industrial way to do that to meet the industrial standard.

 

[danw]

It sounds to me like the A-metalstri-B constitutes a switch.

Wire A-metalstrip-B to a 24Vdc digital input on your PLC, which will attempt to source (or sink) a low dc current (on the order of milliamps) through the A-metalstrip-B circuit and the logic will look for an open or closed condition represented by a one or zero.

 

[strantor]

Mickey mouse concept makes for mickey mouse design, no matter how much you pay for sensors. If a couple of copper studs under the strip are too mickey mouse then I don't think there's any less mickey mouse way to do it, keeping the design constrained to using the strip as a conductor. The only less mickey mouse option I can think of, is a couple of inductive proxes under each end, 2 inputs to PLC, and "complete the circuit" with a rung of ladder.

 

[Tofo]

Mickey mouse concept makes for mickey mouse design, no matter how much you pay for sensors. If a couple of copper studs under the strip are too mickey mouse then I don't think there's any less mickey mouse way to do it, keeping the design constrained to using the strip as a conductor. The only less mickey mouse option I can think of, is a couple of inductive proxes under each end, 2 inputs to PLC, and "complete the circuit" with a rung of ladder.

No. Please don't misunderstand. Using Laser point to point to an eye is stupid. However, there are billion of optical laser sensors. Because the way of those laser sensors have certain types of method to protect operator not to reach the laser point OR the sensors themselves have threaded body for people to mount to uneasy to reach and safety location.


Let me give me what I am think. Does the market have an "multimeter - close loop detection sensor" that guarantee a very low current which would no way to harm any people? <=== This is a not mickey mouse sensor. I think it may be something in the market because I used opto-coupler to isolate power side and signal side when I made a circuit for biomedical device. Those opto-coupler comes with certification and they are approved to use in medical device.

 

[Lancie1]

Does the market have an "multimeter - close loop detection sensor" that guarantee a very low current which would no way to harm any people?

Yes, it is called a switch. The important part in your case for medical equipment is what you connect the switch to. Connect it to an intrinsically safe low-volt, low-current circuit or relay or PLC input, and you should be able to meet all specifications.

If this switching device comes into contact with a human, you could even use a capacitive-sensing switch that will go on when a human touches it with any part of their body, or off it no one is touching the switch. There are plenty of lamps that have capacitive switches that work on this same principle, and is has been proven safe in many appllications.

 

[strantor]

A PLC has a high input impedance just like a multimeter (although not quite as high as a multimeter). With 24v sourcing input, I am not aware of any way this could harm a person, short of driving electrodes into the chest cavity and completing the circuit with the heart. But at that point you have more to worry about. I have never tried it, but I would not be surprised if providing a digital input to a PLC with your wet tongue hurts less than licking a 9v battery. Using 24v sinking inputs there is a chance of sparks one electrode will be connected directly to +24v and if someone shorted it ground, it could spark.

 

[Donvw]

check out antistatic wrist strap on Wikipedia, should help you understand the safety

 

[Tofo]

What if I ask whether any industrial sensor that measure OHM and send signal to PLC? (Please don't tell me an ohmmeter or a multimeter)

 

[daba]

You could possibly use an RTD input module. Those measure resistance.

When the metal strip is in place, the signal would be "in range", and when it isn't, the circuit would be open.

With an "open-circuit", the RTD input module would give an "over-range" reading which would be easy to detect in the PLC logic.

You might have problems with making good connections if the strip is just resting on the contacts at each end.

 

[mendonsy]

You could possibly use an RTD input module. Those measure resistance.

When the metal strip is in place, the signal would be "in range", and when it isn't, the circuit would be open.

With an "open-circuit", the RTD input module would give an "over-range" reading which would be easy to detect in the PLC logic.

You might have problems with making good connections if the strip is just resting on the contacts at each end.

Actually .... that's a good idea!
Another possibility would be to use an analog input set up for 20ma current loop. Most of them have open circuit detection also.

 

[Tofo]

I am sorry that I am not good in this area
May I know what is RTD?
I googled the term. It related to thermocouple