home project

Using type J thermocouples if I would put 3 in series would that give me an average of all 3 points considering that they are within say 10 degrees ?

Is there an easy way (meaning cheap home project)of measuring when a 24vac solenoid is energized with out "tapping" into the circuit,analog OR digital.

Thanks

three thermocouples in series will function just like batteries in series ... their millivolt outputs will be added together and give you a reading which is approximately three times the "correct" output ...

the technical term for this is a thermopile ... from the French word "pile" for battery ... some types of appliances (commercial ovens, etc.) use this approach to generate enough voltage to open a solenoid gas valve, etc. without requiring a connection to another electrical source ...

notice that when you splice the thermocouples together in series, you'll end up with a set of connections (one connection between each pair) that must be kept OUT of the heat zone ... each one of these connections is called a "cold junction" ... basic idea: if you put ALL of the connections of the series loop into the heat zone, then the "cold junctions" will cancel out the "hot junctions" (they'll generate millivolts with the OPPOSITE polarity) ... and you'll get NO additional signal from the extra thermocouples ...

in simple terms: I'm afraid that you're barking up the wrong tree with this idea ...

as for your question:

Is there an easy way (meaning cheap home project)of measuring when a 24vac solenoid is energized with out "tapping" into the circuit,analog OR digital.

Click to expand...

I don't know what you mean ... can you give us some more details? ...

measuring energized solenoid

Easiest it can think of is take your VOM put one test lead on one terminal other test lead on other terminal and read voltage.

You can also hear them click, or if an exposed actuator can see the "shaft" move.

The real question is what do you need or want to do with the information??

Dan Bentler

Without much information, I am guessing your are trying to do something like run a bath or just heat water in general for some purpose? If you are thinking of placing T/C's in at three different points, you will need something to average them (PLC or some stand-alone transmitter), series will not work.

I assume you also want to know if the Solenoid is open to ensure that the water flow has stopped? Use an inline flow switch.

I am taking shots in the dark here based on the little information provided.

guest said:

Is there an easy way (meaning cheap home project)of measuring when a 24vac solenoid is energized with out "tapping" into the circuit,analog OR digital.

Click to expand...

You could glue/tape a magnetic reed switch to the side of the coil. It doesn't get much cheaper than that...

beerchug

-Eric

what if the thermocouples were in parallel ?
The reason for the question is to place multiple tc's outside my house so i can get a true reading not one influenced by sun and thermal radiation.

The 24vac sol. is actualy a gas valve on a heater. So I can watch the runtimes.
I like the reed switch.
Guest

Yes, parallel will give you an average reading. This is commonly
done in the exhaust of turbines ( jet engines )

tcs

Parallel type J thermocouples will give you an averaged reading. But you said "outside your house". The wire distance will probably have enough error that you lose the accuracy that you are trying to use. Type J will oxidize (rust) over time. You might want to use Type T or maybe an RTD. I'd use one sensor and one gas solenoid monitor. It will be close enough.

Some of the newer thermostats now have an energy monitor. The digital display adds up the "gas valve on" running time. That is fantastic and it was in a cheapie $60 stat from Home Depot.

As paul mentioned there are newer type thermostats available that can offer an abundance of information.

As to using the thermocouples outside the house...WHY?
You arent going to heat the outside so that temperature is not relevant, you want to measure room temperatures.

Unless you plan to use a zone heat system I would place the thermostat in the most open and central part of the house. New digital thermostats can be programmed to run specific temps at specific times...ie you work 9 to 5, leave house at 8. Thermostat sets temp to 50 deg F, at 5 it resets it to 70 deg F so when you get home at 6 its warm again.

The only way to maintain a set temp in each room is by use of zone controls....which gets elaborate.

A cute, simple, cheap trick with an external and internal thermocouple: wire 2 in series, but inverted (+--+). You'll get a signal of the differential. You can feed the mV into any process meter and scale it. For example: when the difference is only 5 degrees and decreasing, turn off furnace. When 30 degrees and increasing, activate secondary home heating source (such as nat gas which is more efficient that a heat pump when it is really cold outside.) That's just an example.

When getting a programmable Tstat, don't go too cheap - make sure they have a battery backup so that when there is a power interruption, it does not loose it's programmed values.

This may save spousal relations if you happen to be out of town on business and the local power company has a slight discontinuity in service even for an instance.

So...

The actual temperature in three rooms are...

...Bedroom-1 = 30-degrees (brrrrr....)
...Bedroom-2 = 100-degrees (pant, pant, sweat...)
...Livingroom = 72-degrees (oooo... ahhhh...)

The average temperature is... 67.33-degrees... If the Set Point is 72-degrees then the heat will come on...

Your guest in Bedroom-1 will think, Damn! It's about time...

Your guest in Bedroom-2 will think you really meant it when you said you wanted to have her for dinner... stick a fork in 'er Clancy... she's done!

The other guests in the Livingroom will be wondering... What the hell? Why is the heat on? The temperature was perfect!

Use your thermocouples, individually, to control the registers in each room. Also use the thermocouples to monitor for demand. As long as there is any demand, keep the heat on.

The same logic applies to air-conditioning.

Be careful to keep the heat-mode and A/C-mode from overlapping.

You arent going to heat the outside so that temperature is not relevant, you want to measure room temperatures.

Click to expand...

You use the outside temperature to change the setpoint of the water in the boiler - colder outside higher setpoint so as to raise the available energy from the radiators to compensate for the higher heat loss through walls and windows (~proportional to temperature difference), not so cold outside, lower setpoint. German central heating systems have been using this for decades to improve heating efficiency.

Ah yes, I forgot, Americans aren't interested in energy efficiency!

Just one thing most gas boilers run at peak efficiency when the process water is as hot as you can get it without boiling , radiators run well balanced with a delta T of about 6-10 C , and the rated output is generated at that . boiler too cold , loads of waste , heat used to remove flue gas condensation on the heat exhanger first.
run the bugger hot , unless of course it is a condensing boiler
You could of course zone it , and better still individual TRV's on each rad

This is not true of modern fan controlled heat-modulating boilers. The most modern boilers available in Germany (i.e. manufactured within about the last ten years) achieve effiencies of typically 103% (for oil) to 106% (for gas), because of the way the heat content of the fuel is defined. They achieve this by recovering the condensation energy out of the water vapour which condenses in the chimney. The exhaust gas is so cool (<50°C) that you can put your hand on the exhaust without getting burnt. A typical boiler for a modern family home of, say, 120 qm will have a rating of 12 - 13 kW as opposed to over 20 kW a few years ago (30% or more of which, disappeared up the chimney).

Current building regulations require a normal family home to use no more than 30 kWh/qm/year - equivalent to 3 litres of oil. This means your typical 120qm home will require 360 litres of oil per year. Before 1995, when they started tightening up the requirements (yes for Kyoto, amongst other things), a typical house would have used between 140 and 200 kWh/qm/y. So your typical house would have required between approx 1700 and 2400 litres of oil / year. Since oil isn't getting any cheaper, this is not just leading to decreasing CO2 output, it's also saving hard cash.

Oh, by the way, if you have an older house and you decide to renovate it, or build on to it, not only do you have to meet the current standards (which is pretty obvious really) but if the area involved is more than 20% of the original living area of the house, the whole house has to be brought up to the new standard - that can get VERY expensive indeed - to the point where I'm not sure that it might not be counter-productive!

and better still individual TRV's on each rad

Click to expand...

is considered self-evident over here. Many people, including myself, use the kind where you can program the times where you want the full heat, for example in the bathroom for an hour or so in the morning (a different hour at weekends, of course) and then slightly cooler for the rest of the time. This is in addition to the normal overall boiler temperature reduction at night.