| T O P I C R E V I E W |
| gtfoxy |
Posted - Dec 28 2008 : 7:26:49 PM
I did some searching and the only thing I could find was related to amps.
I am looking for a way to trigger a series of relays with a Low voltage Signal. I will be using a Type K thermocouple to trigger a relay at ~20mV. Any retailers, supply places or schematic ideas for getting this accomplished would be awesome!
I am hopeful I can find the help I need for this.
Thanks in advance! |
| 2 L A T E S T R E P L I E S (Newest First) |
| gtfoxy |
Posted - Dec 29 2008 : 12:22:32 AM
Good thought. Modern home type furnaces have a flame sensor that is ran through a circuit board to trigger the valve. The board looks at inputs from a pressure sensor, and input voltage at L1 before it will trigger the valve opening. One burning it will look for the Flame sensor to keep the valve opening. I am not sure of the type of coupler they use, however, it gives me something to experiment with. I also have more than a passing familiarity with R.V. 12V furnaces which also happen to work in much the same way. I just happen to have a few spare 12V boards laying around my shop I can experiment with. They also have a sail switch which can deactivate the valve if temps get to hot. That is a low range temp switch compared to what I am working with though. I gues it is the mV output I am more concerned with as it relates to the board triggering the valve relay.
(Edit) I did some thinking last night when I went to bed, On a 12v Furnace the Valve is triggered only by the T-stat input and the Fan switch input. The sail switch is a simple 12v pass through switch. These are also the same boards used in Suburban and older Atwood R.V. 12V water heaters. They, however, have an addition input on the board from a reastat. This way when the first reastat input is lower than water temp, it triggers the valve, when the reastat sees a certain temp, it shuts down the valve. This was usualy adjusted by either a knob on the valve or a radial moving lever, also located on the valve, to set the temp range of the water in the tank. Newer Atwoods use two individual temp switches, one high, and one low. They are removeable and are changeable for a desired water temp. They still however operate the same way, as a 12V pass through switch. So needless to say, not quite what I am looking for. The method is correct, for what I am looking for, not the Voltages.
What I am trying to do is: Use this in a start sequence on a trubine engine. I want to engage a start sequence and have an EGT input shut down the start sequence when adequate chamber temp is present to have a sustained burn inside the engine. I can get around doing this by simply using a time based start sequence, however, I do not want the start sequence going on longer or shorter than is required. This time will change depending on relative ambient temperature and the fuel used. There might be a way to have a temp input into a logic board that can refference to a table for start sequence times based on Temp and the fuel used. This would work but at the cost of more expensive and time consuming programable electronics which I have limited familiarity with. Not to mention, if I can get the EGT input to work, there is no reason to go through all this trouble and added expense.
Maybe I am splitting hairs and start sequence will be well under 20 seconds or so. It might just come down to experimentation.
If anyone else has any input I would appreciate it. |
| audioguru |
Posted - Dec 28 2008 : 9:44:43 PM
I think my home furnace and gas fireplace have a thermocouple driving a solenoid gas valve. I don't know if your thermocouple is in a hot flame and I don't know how much current it gives and I don't know how much is the current required for the solenoid. |
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