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The thermocouple responds to changes in temperature by producing an electrical current that causes the gas valve that supplies the pilot light to open when the temperature is high or to close when there is no direct heat source.
How does a thermocouple actually work?
A thermocouple is a sensor that measures temperature. It consists of two different types of metals, joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created that can be correlated back to the temperature.
How does a gas burner thermocouple work?
It contains a metal rod that is placed very close to your pilot light’s flame. When your pilot light is lit, the heat from the flame sends a voltage through the thermocouple that keeps the gas line open. If the pilot light goes out, the thermocouple will lose its voltage and the gas line to your furnace will be closed.
What makes a thermocouple go bad?
Soot buildup on the thermocouple may block the flame. Under constant exposure to a hot flame, a thermocouple wears down over time. Even a slight residue can make the thermocouple malfunction.
How does a thermoelectric gas valve work?
How it works: Thermoelectric gas valve is controlled by the thermocouples DC voltage (figure 2). The valve receives the DC voltage that the thermocouple generates by being heated and magnetizes the power cell located inside the body of the gas valve.
Can I bypass a thermocouple?
Realistically, you have just disabled the thermocouple, but you can also reach in and unclip it from its holding bracket where it meets the pilot light. In most cases it will be held on with a gravity clip, but some are held on with a screw that must be removed with a small screwdriver.
Does a thermocouple require power?
A thermocouple is a temperature sensing device consisting of two dissimilar metals joined together at one end. In contrast to most other methods of temperature measurement, thermocouples are self-powered and require no external power supply.
Does the thermocouple open a solenoid valve or hold a solenoid valve open?
A thermocouple is a type of flame safety that prevents the gas valve from dispensing the gas into the burners without the presence of a flame. If the flame goes out, the solenoid will close and stop the flow of gas as the thermocouple will not generate the amount of voltage (millivolts) to hold it open.
How do you test a thermocouple?
Place one test lead on the side of the thermocouple and the other to the end that screws into the gas valve. If the thermocouple has proper continuity, a small resistance reading should be visible on the multimeter. Many multimeters also indicate continuity with an audio alert.
Should the thermocouple be in the flame?
The flame should strong enough to cover about 1/2 inch at the end of the thermocouple tip. If the flame is too strong and not adjusted correctly, it will be blue and may make a hissing sound as the flame crosses the thermocouple.
What does a bad thermocouple look like?
Before jumping to the conclusion that the thermocouple is at fault, look at the pilot flame. If it appears small and has an orange-yellow tinge, it may be too weak to heat the thermocouple. The likely problem, again, is an obstruction in the pilot tube.
Can you damage a thermocouple?
Like the other component parts in your furnace, the thermocouple can wear down over time, producing lower voltage than it should when heated. And the worst part is that you can have a bad thermocouple without even knowing. Therefore, inspecting and testing your thermocouple should be part of your furnace maintenance.
How does a gas safety valve work?
As the igniter heats up, it warms a bimetallic strip inside your gas oven safety valve. When the igniter reaches its operating temperature, the bimetallic strip opens the valve and allows the gas to flow, igniting as it crosses the heated surface.
What does th and Tr mean on a gas valve?
Th is thermostat. Tr is transformer. If there is a third terminal that is Th/Tr then both a wire from the transformer and the thermostat can go on it just as a convenience terminal.
Can a thermocouple be cleaned?
Yes, you can clean a thermocouple, but the task must be done with a light touch. Remove the thermocouple from the process assembly, using a steel wool or emery cloth, lightly clean the tip removing any build up. Cleaning a thermocouple is not a fix for an issue, such as inaccurate readings.
Why will my gas logs not stay lit?
The thermocouple and thermopile are the two most common reasons why a gas fireplace won’t stay lit. However, there are other possibilities out there. Another common culprit is incorrect gas pressure. As the seasons pass, you may find that your gas pressure drops below where it needs to be.
What does a dump switch do?
A dump switch is a safety device on propane heaters that shuts off the gas if the heater gets knocked over. When the heater is standing upright, a small weight inside the dump switch presses down, completing the circuit and allowing gas through to the heater.
Is a thermocouple passive or active?
Examples of passive sensors are thermocouples and photodiodes which generate thermoelectric voltages and photocurrents, respectively, which are independent of external circuits.
Does a thermocouple produce AC or DC voltage?
Figure4 shows also the filtering and amplification of the thermocouple. Being the thermocouple voltage a DC signal, removal of AC noise through filtering is beneficial; furthermore the thermocouples produce voltage of few tens of mV and for this reason amplification is required.
How is voltage generated in a thermocouple?
When two dissimilar metal wires are joined, the difference in the energy levels of the electrons in each metal causes electrons to migrate from one metal to the other and a voltage (EMF) develops. This voltage is dependent on temperature.
Are thermocouples and thermopiles the same thing?
The main difference between Thermocouple and Thermopile is their method of measurement. The thermocouple is a thermoelectric instrument, while the thermopile is an instrument that modifies thermal energy into electrical output.
