Telephones

Hi guys I know that this is a plc site but I needed an answere quick and I know you guys are good!

I have a 35mV audio output and I need to boost it to a 5V output to energize a relay.

We have a sounder in a different room that we have used to be able to hear the phone if its ringing. It is a Zone 1 area where the sounder is so anyold circuit could not be used initially. So I now have the dilema of converting the speaker output into something that will enegize the relay and active the sounder.

Any ideas? please please help

Cindy

None of these will work?

http://www.phonemerchants.com/telsigdev1.html

Vetteboy

Hi Cindy,

I do not have direct experience with Zone 1 equipment, but I believe that could route your 35mV signal to your "safe" zone and then use a signal amplifier get your 5V. The one thing I think you will need to do is to make sure your 35mV signal is intrinsically safe (by adding a zener diode?) in the proper location (at the source, I believe).

Phoenix Contact, for example, has a bunch of options in there Interface catalog. One of them is the MCR-C-UI-UI-DCI Configurable 3-Way Isolating Amplifier. With it, it appears you could configure it for 0-60mV in and 0-10V out. That way your 35mV would equal just over 5V.

Steve

Intrinsically safe or flameproof

Cindy,

You're right in saying any 'ol circuit won't do. Zone 1 is a hazardous location roughly equivalent to Class 1 Div 1 area locations here in the US (although we are starting to adopt the IEC classification schemes).

You didn't mention if the sounder was either an Intrinsically Safe or a Flameproof (Explosion proof) unit. Looking on the sounder in the Zone 1 area you should see some letters like "EEX ia" for I.S. equipment and "EEX d" for Flameproof. Also you didn't mention what power supply the sounder needs to operate.

For I.S. equipment it is possible that either a galvanic isolator or possibly a zener barrier could work (there are several items needed to know before these could be specified such as wire length between the isolator, type of power supply and ratings, as well as the electrical ratings of the sounder itself). Try looking at MTL (http://www.mtl-inst.com/) or pepperl and fuchs (http://www.pepperl-fuchs.com/pa/welcome_e.html) or run a search in google for suppliers nearest you. I reccommend using a commercial made barriers / isolators instead of rolling your own as they have been specifically designed for the task (triplicated diodes + insulation + fuses + potting etc.... and unfortunately $$$$, but thats the cost for that equipment) and a home grown one would not be within compliance.

If Flameproof then you might get away with just a signal isolator (the suppliers should also be able to help you out with an isolator for that as well).

In any event you might want to research the installation requirements for Zone 1 areas that your plant uses to ensure that everything is installed correctly. I remember the time I was in So. America in a propane tank farm with one of the plant engineers telling me the entire installation was CL1 Div I as I saw parts of the electrical installation that certainly was not in compliance. Needless to say that was the quickest field service call I have ever made in my life!

Good luck!

Wouldn't a Piezo device like a Sonalert work without the amp??

David

Go to http://www.sandman.com/wizard.html This guy has EVERYTHING, and it all works!

Intrinsically safe

Cindy,
You need to make sure your total circuit current is less than 93ma to be able to use any of the intrinsically safe barriers, the device that you are driving should also be listed as approved equipment to use in an intrinsically safe circuit. One other alternative is to purge the equipment in the hazardous area.

Can you be a little bit more specific in what you want to acheive. Maybe because it is early in the morning and my eyes are tired.

If the voltage is on the sounder in the Zone 1 area then LEAVE IT ALONE!!! Circuit modification will render the unit unsafe in the eyes of the HMI and the person making the modification liable to a maximum prison sentence of 10 years.

If you want a telephone sounder in the zone 1 area then visit www.e-2-s.com for an FLP Ex 110-240ac powered unit.

Why not go for an IS telephone, cost around £700 from RSWWW.com

Martin

I should have been clearer

Sorry guys I guess I should have been a bit clearer on the situation.

I have a sounder in a zone 1 area, this has been wired to a relay box in a safe area (no zone required). All this work was done by outside contractors, we had told them that the phone voltage across the ringing speaker was 5V, so they baught a relay that would work on 3 to 9V to switch the sounder on when the phone was ringing.

But...we done have 5V we have 35mV. So I need to come up with a circuit that can boost an audio signal of 35mV to 5V. I can build the circuit myself but as for desiging it well I've lost touch with all that and I cant remember, I know I need an audio amplifier of some sort but then there is other circuitry that will be required resistors, capacitors?

I have looked into the purchasing of the other devices that you have pointed me towards but the company is not happy spending more money on something which should have worked already.

Cindy

Sounder

I've done similar items the way U-R talking, U might want to go by Radio Shack & explain it to them they should be able to acomidate Ur requirements, with an amplifer.

op amp comparator circuit

Take a look at this site, it should help you out a bit. - If anything it should at least get you going in the right direction. You'll have to work with the cicruits a bit to get the set points you need.

I would not drive a relay directly off of an op amp output - use a switching FET to do that - there are relay driver FETs available from the manufacturers (Harris, Motorola etc...)

http://www.swarthmore.edu/NatSci/echeeve1/Class/e72/E72L2/Lab2(OpAmp).html