Relay Coil That Runs on mV of AC

Not without some form of interface. It takes a bit of wallop to get a solenoid to operate, and for that something more than a few mV would be needed.

Relay that runs on mv AC, sorry i dont think any sane manufacture would design and make one.

What voltage or should i say Milli volt would you want this to operate at? and why?

You could use a PLC that has an analouge input to convert the signal into a usable output with the right software, but you would probally have to use a thermocouple analogue converter before it was connected to the PLC, this would depend on the operating voltage that you want the unit to use, at least this way you will have some control over switch on and switch off voltages, any other way you may have no accurate control over the switch off/on voltage due to the ability of the holding power of the relay.

Sorry mate i wish i could be of more help, but that is all i have got.

May the force be with you.

You may have to use multiple relays to step up the the voltage to the coil on the final relay. www.omega.com tech support will tell you how their products can achieve your goal.

Just another thought, you could use a resister to convert mv to V.

example; 250 ohm resister with 4 to 20 mv will give you 1 to 5 volt

This way you can find a relay than can be opporated by 5 volt coil if you had 20 mv.

No it won't. You're confusing current with voltage. 4 to 20 milliamperes into a 250 ohm resistor will produce 1 to 5 volts. If the OP mistyped and meant mA to V then you could detect using this approach but as others here have stated this may not be enough power to engage a relay's contacts. The OP's original question certainly does not have enough information to provide an accurate answer.

Yes, like I said I should have finished my coffee first. I was thinking mA.

Any way he got his answer with the Honeywell gas valve.

Nah; honeywell & many others made a gas valve that operated from the millivolt pilot light thermocouple. perry

Yes, you are right. I missed the fuel valve part and was focused on the first reply and I like a challenge and did not have my coffee yet. A source for the honeywell mv gas valve are @ http://www.pexsupply.com/Honeywell-VS820A1336-Standard-PowerPile-Millivolt-Combination-Gas-Valve-3-4-NPT-x-3-4-NPT-13864000-p

Thanks, all. ..

Hello Electroman,

I hope you are fine?

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Just about every gas appliance uses a thermocouple to hold open the primary gas valve...

If the pilot light goes out the relay drops out and cuts off the gas.

The thermocouple is dc but in the mV region, the coil is several turns of large guage wire on a former that holds the valve open against a spring... Due to the low impedance of the coil many amperes flow - enough to actuate the valve.

I find this small piece of information is interesting, and, crucial!

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GA to you Sir.

Why thank you sir.

I have been told its impossible by other engineers, for a thermocouple to have enough power to actuate this valve in the way I've described....

Yet they are fitted and do indeed work to almost every gas appliance made...

PS I was sceptical at first until a customer I visited showed me now it worked...

Yes a GA. Utilizing the near ideal battery characteristic of a bimetallic thermocouple. But as somebody else pointed out, the relay would have to have very fine wire with a lot of turns to open that valve.

In operation I guess there must be a mechanical bypass button used to start the gas initially.

There is....

Ever wondered why most gas appliances you have to push the knob in to be able to turn it?

This is to push the valve against the electromanet to open the valve, if the thermocouple is hot enough the valve is held open, if not the valve closes as soon as you release the knob.

See my other post about needing to use thick gauge wire to get enough current to flow...

You're quite correct about the wire gauge. I just drew up a few quick equations, it is a little counter intuitive. Less turns but more than one around the solenoid core does produce the higher magnetic field versus resistive load losses. I retract my earlier critique, nice GA.

Practical when superconductivity becomes practical.

Guest wrote: Practical when superconductivity becomes practical.

Suggest you review some technical history. Thermocouple operated valves have been a part of every gas fuelled appliance for many decades. I learned about them back in 1967 and it was old technology back then.

However I have a question to MasterBlaster. Millivolt input but a large gage wire size in the coil? I don't think so. Every gas valve I have ever dissasembled had vary fine small gage wire in the coil of the fuel shut off valve. The many turns is needed to make the millivolt input effective. Did you mean something else?

I think you are mistaken my reply for someone else's. I admitted that I miss-read mV for mA and I said nothing at all about large gage wires. If you read through the thread you will see that I eventually sent a link to a Honeywell gas valve.

The original question said nothing about a thermocouple couple operating a valve, or how many mV, so I pictured a mA (it was mV but I did not have my coffee and thought mA), signal that needed to operate a solenoid valve. I have used mA signals through a resistor to get DC volts to operate other relays or devices.

You must not have had your coffee either because it was "Electroman" that talked about large wire. Which is a relative statement. How large is large?

What part of Western Canada you from? Alberta

elnav if you were to use very fine wire you would have a high coil resistance which would mean that a few mVolts will only pass microamps - not enough to operate a solenoid.

So Yes the wire is large at about 16 swg or 1.6 mm to give a very low resistance so that a large current can flow, even with only millivolt signals...

Remember its the current that generates the magnetic field, ampere turns etc...

I stand corrected. But being from western Canada I had to see it for myself. So I disassembled a Robertshaw gas valve from a Coleman furnace. The pilot valve coil powered by the thermo couple was 16 - 18 Ga wire; 10 turns of approximately 5/16" diameter coils. Couldn't fit a wire gauge into the space and did not want to destroy the valve completely. And the thermocouple delivered 28.1 mV .

Now to me #16 is a relatively fine wire compared to the power stuff I usually work with. But that is a semantics quibble. The fuel valves I was thinking of were powered by 24V. Which makes a big difference.

elnav, I did exactly the same, after seeing the demonstration at the customer's premises, I had numerous samples that we had to design leak testing equipment for and so I dismantled one...

I was quite surprised at my findings the same as you sound like you experienced.

That was 15 years ago and I thought I knew about most things then - its a reminder of how we are always learning things....

Speaking of thermo couples. Just how much amperage does it develop? It certainly looks like amps not milliamps.

On a related note, there is a radio repeater tower near us. I was up there berry picking and got curious about the continuous sound of a burner going. This on a very hot July day. The shack is supplied by a pair of 1500 L propane tanks. Exterior to the shack is a furnace like device made by the thermo corporation.

It looks like they are burning propane to generate power for the radios. Most likely some kind of thermocouple device that generates enough steady power to charge a battery bank which then powers the radio transmitter which is cycling, not running steady. The waste heat (after generating power) can then be used to heat the building in winter or dumped in summer. I was unable to find a website for the company.

Hello elnav,

When you need to check on the thickness by dissembling a gas valve, it all becomes clear, right? As in:

HEAR & you forget <-> SEE & you remember <-> DO & you will understand?

Take care............

That is the way I have always done it. Taught myself about gasoline fuel injection by getting a fire wrecked Porche. Dismantled everything. I usually ask service people I know to save me the old replaced modules. There was a chemical company in Conneticut that had an epoxy dissolving compound. I used it to unpot encapsulated modules. Then traced out the circuit.

Was always mindful of that line when I was teaching. I tried to give as much hands on to my students as possible.

Hi elnav,

It is the best way to learn if you have the mind to figure out things as you go. I like the epoxy dissolving idea, would never have thought of that!

Hello Nah,

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Please see the search site directly under this:

http://www.google.com/search?client=safari&rls=en-gb&q=Coil+specification+for+boiler+gas+valve+running+on+millivolts+AC+electric&ie=UTF-8&oe=UTF-8

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Below is some sites taken from the search. I hope this helps.

[PDF] 68-0170 - T8112 Programmable Thermostat File Format: PDF/Adobe Acrobat The specifications given in this publication do not ... Gas—Electronic Ignition. Yes. Gas-Fired Boilers. Yes a. Gas—Millivolt ... All wiring must comply with local electrical codes and .... When the batteries are running low, a bAt Lo indicator will .... such as the gas valve, zone valve, or oil burner control. ... mas0000.dealerstack.net/T8112_Product%20Data.pdf

- Similar - Heating, Air Conditioning, Fridge, HVAC - Home Appliances - Home ... 21 Feb 2009 ... Once the gas valve has opened there is just a . ... old goodman 5 ton ac ( outside) with a goodman 20 kw electric heat unit (inside). the . ... en.allexperts.com/q/Heating-Air-Conditioning-696/index_506.htm

- Similar -

[PDF] 68-0170 - T8112 Programmable Thermostat File Format: PDF/Adobe Acrobat specifications. Also, this product is tested and .... Gas—Electronic Ignition. Yes. Gas-FiredBoilers. Yes a. Gas—Millivolt .... Electric Furnace—leave at the Warm Air Furnace setting... When the batteries are running low, a bAt Lo indicator will .... such as the gas valve, zonevalve, or oil burner control. ... [n]www.air-n-water.com/manuals/t8112dmanual.pdf

- Similar -

[DOC] PHILOSOPHY AND IMPORTANCE OF MONITORING BOILER PARAMETERS File Format: Microsoft Word - View as HTML The cooling water & necessary electrical supply upto the SWAS package will be ... The chiller should meet the specifications given below : ... Coolers used in the chilled water circuit shall be submerged helical coil type and tube design ... Secondary cooler must be provided with relief valve in addition to relief ... www.forbesmarshall-inc.com/.../Specifications-TPS- Super%20Critical%20Once%20through%20%20Boilers_2008.doc

- Similar -

[PDF] 10538 QSV81G Data Sheets File Format: PDF/Adobe Acrobat - View as HTML Specifications May Change Without Notice. 05/01 CPG QSV81/C ... drive throttle valve q. CENSE engine monitoring system. Ready Filled ..... standard on MV and HV). Fuel System.Gas flow meter. Pressure regulating valves. Flexible connecting pipe ... Exhaust gas boilers. Separate lubricating oil cooling circuit ... www.proidea.hu/cad-server-86336/cummins...243368/1370.pdf

- Similar -

Borg Warner with Honeywell ignition Buzzing [Archive ... You may find it easiest to remove the pilot tubing at the gas valve with a 7/16" ... chart between identification number and order specification number. .... I know the easy answer is don't bend the tube, but it comes in a coil so its ... If you disconnect MV, the pilot will light, the spark will stop but the main ... forum.doityourself.com/archive/index.php/t-380635.html

- Cached - Similar - [PDF] 68-0148 - T8131A,B,C; T8132A,B,C Programmable Thermostats File Format: PDF/Adobe Acrobat match the listed specifications. Also, this product is ... Gas—Electronic Ignition. Yes. Gas-Fired Boilers. Yes a. Gas—Millivolt .... COIL. FAN. RELAY. HEATING. RELAY OR. VALVE COIL ... As the batteries are running low, a "bAt Lo" indicator .... primary control, such as thegas valve, zone valve, or oil burner ... customer.honeywell.com/techlit/PDF/68-0000s/68-0148.pdf

- Similar -

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Good luck and I hope this helps.

As long as we're on the subject of amp-turns:

the old electromechanical voltage regulators had a current sensing relay to limit DC gen. current, which coil consisted of a few turns of heavy wire. This kind of relay would certainly come in handy today for sensing motor current. Does anybody make one?

I know there are electronic versions of current-activated switches but a low tech relay would work just fine for a lot of applications.

BTW, HVAC techs wanted to know if they could test gas valves by using a 1.5v cell. Somehow I determined that 28 mV gas valves use 75 mADC to work, so the answer was that they shouldn't use a cell.

You guys are tenacious!

Thanks.

Hello Nah,

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the old electromechanical voltage regulators had a current sensing relay to limit DC gen. current, which coil consisted of a few turns of heavy wire. This kind of relay would certainly come in handy today for sensing motor current. Does anybody make one?

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http://www.statemaster.com/encyclopedia/Galvanometer

This is the sites address. You will see information on a camera and a picture of a Galvanometer there. With explanations which I have not pasted here.

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I believe you refer to a 'Galvanometer'. As the pasted piece below shows these units are available in certain 'everyday' items used regularly. The exact name given I think you may see depends on whether you might want to measure AC or DC, and or measure by 'touching' or by some predetermined distance.

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I have pasted the piece below as it is so interesting. I can understand Engineers may know these things are in regularly used items in every home, but, I doubt if the 'average Joe' will?

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Galvanometer:

Wire carrying current to be measured

Restoring spring

N and S are poles of magnet

A galvanometer is a type of ammeter — an instrument for detecting and measuring electric current. It is an electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through.

Contents

1 History

2 Operation

3 Types

3.1 Tangent galvanometer

3.1.1 Theory

3.1.2 Geomagnetic field measurement

4 Uses

5 References

6 External links

History

The term "galvanometer" derives from the surname of Luigi Galvani. Many early applications of galvanometers for measuring and recording are associated with William Thomson (Lord Kelvin). The earliest galvanometer was reported by Johann (Johan) Schweigger of Nuremberg at the University of Halle on 16th September 1820. André-Marie Ampère also contributed to the development of the galvanometer.

Operation

The most familiar use is as an analog measuring instrument, often called a meter. It is used to measure the direct current (flow of electric charges) through an electric circuit. Such devices are constructed with a small pivoting coil of wire in the field of a permanent magnet. The coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position. In some meters, the magnetic field acts on a small piece of iron to perform the same effect as a spring.

When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts with or against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer so that the pointer position smoothly tracks the current without excess vibration.

((This unit described below has a picture with it but I am unable to paste the picture)).

An automatic exposure unit from an 8 mm movie camera, based on a galvanometer mechanism (center) and a CdS photoresistor in the opening at left.

The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current).

Such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude.

The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents. A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full scale current.

A meter can be configured to read other voltages by putting it in a voltage divider circuit. This is generally done by placing a resistor in series with the meter coil.

A meter can be used to read resistance by placing it in series with a known voltage (a battery) and an adjustable resistor. In a preparatory step, the circuit is completed and the resistor adjusted to produce full scale deflection. When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously-unknown resistor.

Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by moving the head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator's eye must be directly above the pointer and any parallax error has been minimized.

Types

Extremely sensitive measuring equipment once used mirror galvanometers that substituted a mirror for the pointer. A beam of light reflected from the mirror acted as a long, massless pointer. Such instruments were used as receivers for early trans-Atlantic telegraph systems, for instance. The moving beam of light could also be used to make a record on a moving photographic film, producing a graph of current versus time, in a device called an oscillograph

Galvanometer mechanisms are used to position the pens of analog chart recorders such as used for making an electrocardiogram. Strip chart recorders with galvanometer driven pens might have a full scale frequency response of 100 Hz and several centimeters deflection. In some cases (the classical polygraph of movies or the electroencephalograph), the galvanometer is strong enough to move the pen while it remains in contact with the paper; the writing mechanism may be a heated tip on the needle writing on heat-sensitive paper or a fluid-fed pen. In other cases (the Rustrak recorders), the needle is only intermittently pressed against the writing medium; at that moment, an impression is made and then the pressure is removed, allowing the needle to move to a new position and the cycle repeats. In this case, the galvanometer need not be especially strong.

Tangent galvanometer

A tangent galvanometer is a measuring instrument used for the measurement of electric current. It works on the basis of the tangent law of magnetism. It was first described by Claude Servais Mathias Pouillet in 1837.

A tangent galvanometer consists of a circular coil of insulated copper wire wound on a circular non-magnetic frame. The wire connected to the tangent galvanometer has to be wound, otherwise the field due to the wire will affect the deflection and an incorrect reading will be obtained. The frame is mounted vertically on a horizontal base provided with levelling screws on the base. The coil can be rotated on a vertical axis passing through its centre. A compass box is mounted horizontally at the centre of a circular scale. The compass box is circular in shape. It consists of a tiny, powerful magnetic needle pivoted at the centre of the coil. The magnetic needle is free to rotate in the horizontal plane. The circular scale is divided into four quadrants. Each quadrant is graduated from 0° to 90°. A long thin aluminium pointer is attached to the needle at its centre and at right angle to it. To avoid errors due to parallax a plane mirror is mounted below the compass needle.

THEORY

When current is passed through the tangent galvanometer a magnetic field is created at its corners given by where I is the current in ampere, n is the number of turns of the coil and r is the radius of the coil.

If the TG is set such that the plane of the coil is along the magnetic meridian i.e., B is perpendicular to BH (BH is the horizontal component of the Earth's magnetic field), the needle rests along the resultant. From tangent law, B = BHtanθ, i.e.

or I = Ktanθ, where K is called the Reduction Factor of the tangent galvanometer.

The value of θ is taken at 45 degrees for maximum accuracy.

GEOMAGNETIC FIELD MEASUREMENT

A tangent galvanometer can also be used to measure the magnitude of the horizontal component of the geomagnetic field. When used in this way, a low-voltage power source, such as a battery, is connected in series with a rheostat, the galvanometer, and an ammeter. The galvanometer is first aligned so that the coil is parallel to the geomagnetic field, whose direction is indicated by the compass when there is no current through the coils. The battery is then connected and the rheostat is adjusted until the compass needle deflects 45 degrees from the geomagnetic field, indicating that the magnitude of the magnetic field at the center of the coil is the same as that of the horizontal component of the geomagnetic field. This field strength can be calculated from the current as measured by the ammeter, the number of turns of the coil, and the radius of the coils.

Uses

Use of galvanometers declined late in the 20th century, largely replaced by time-domain reflectometers for finding faults in telecommunications cables.

Mirror galvanometer systems are used as beam positioning elements in laser optical systems. These are typically high power galvanometer mechanisms used with closed loop servo control systems. They can have frequency responses over 1 kHz.

Galvanometers have been replaced as measuring instruments by analog to digital converters (ADC) for most uses. There are, for instance, self contained digital measuring systems, called digital panel meters (DPMs), available to replace most traditional analog meter functions.

References ^ http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Tangent_Galvanometer/Tangent_Galvanometer.html

External links

Selection of historic galvanometer in the Virtual Laboratory of the Max Planck Institute for the History of Science

Results from Fact Bites:

Galvanometer - LoveToKnow 1911 (2114 words)

A ray of light being thrown on the mirror from a lamp the deflexions of the needle were observed by watching the movements of a spot of light reflected from it upon a fixed scale.

The movable coil galvanometer has the great advantage that it is not easily disturbed by the magnetic fields caused by neighbouring magnets or electric currents, and thus is especially useful in the electrical workshop and factory.

In the construction of a movable coil galvanometer, it is usual to intensify the magnetic field by inserting a fixed soft iron core in the interior of the movable coil.

Spartanburg SC | GoUpstate.com | Spartanburg Herald-Journal (1394 words)

The earliest galvanometer was reported by Johann (Johan) Schweigger of Nuremberg at the University of Halle on 16th September 1820.

In some cases (the classical polygraph of movies or the electroencephalograph), the galvanometer is strong enough to move the pen while it remains in contact with the paper; the writing mechanism may be a heated tip on the needle writing on heat-sensitive paper or a fluid-fed pen.

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I think this is understandable without the pictures. However if you need it, the site's address is just under the bold hatched line

which delineates your copied post, from the start of my own explanation near the top of the page.

You know it's in exchanges like this where I learn so much more than I thought I knew...I think this is why I (and I'm sure, others) read CR4 as often as possible. No one really knows where the next piece of understanding will come from....

More data, more understanding.

Hello Sparkchaser,

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I hope you are well?

Just to say I absolutely agree with what you say! :=)

Reading the kind of knowledgeable posts I know I will find on CR4 in reply to most questions, for me is so informative. One post leads to another and then, a link will be added, then you get into finding even more detail. Brilliant!

Take care.................