Troubleshooting Problems with a Gas Furnace Thermocouple Written by Doityourself Staff. No two batches of wires are exactly alike. © 2021 WIKA Alexander Wiegand SE & Co. KG. In many cases, if the thermocouple is the source of a problem, it … If your pilot light ignites but won’t stay lit, then the problem is most likely related to your thermocouple, a metal sensor (about the size and shape of a sharpened pencil) that heats up by direct contact with the pilot light’s flame, telling your gas valve that the pilot light is lit so it’s safe to open the valve to let gas flow. This is the measuring junction. thermocouple to the ADC should be simple and symmetric to avoid unintentional thermocouple junctions. Here is a brief list of some of the most common thermocouple problems. If the resistance value shown on the multimeter is large, it indicates that the internal connection of the thermocouple is open, so replace the same type of thermocouple. This is a common error, as there are numerous types of thermocouples – types K, J, N, E, T, R, S, and B – each with a different range, accuracy, and electrical output. If the heat isn’t detected, it cuts off the flow of gas, keeping your household safe. Most likely, you have the thermostat set too high. That’s a good thing since it keeps your home from being flooded with gas, but it also means you won’t have access to your heat until it’s fixed. All fields are required. Thermocouples are among the most popular temperature measurement instruments in industrial applications because of their versatility and ease of use. As mentioned before that this device will convert the thermal energy to the electrical energy, no wonder that it … Maximum exposure temperature, cyclic measurements, and frequency of the cycles affect the metallurgy with a resultant drift, usually downward. This article discusses the six most common causes of thermocouple errors. Thermocouple. If you accidentally reverse the polarity of the thermocouple lead wires, the measured temperature will be incorrect by the difference in temperature of the two ends of the leads. Thermocouple measurements DMM ZH Metal A H Metal B Icom L ZL 1. The most common thermocouples are types E, K, J and T, which are ‘Base Metal’ versions. Although thermocouples are reliable, temperature measurement errors can occur for various reasons. Watch out: failure to place the tip of the thermocouple in proper position to sense the gas pilot flame is a common source of heater troubles and failure to operate. Otherwise, there is a certain resistance value, indicating that there is something wrong with the input end of the instrument, and the instrument should be replaced. The linearity must be corrected for almost any practical use of a thermocouple. At higher temperatures the electrons gain kinetic en… Pilot light issues. How Can a Heat Pump Heat When it’s Chilly Outside? However, measurement errors can occur. Get your fireplace inspected and repaired. The common problems of thermocouple wires and solutions as attatchment. As the thermocouple signal connects to the ADC integrated circuit, each step along the path can encounter several additional thermocouples. Our website uses cookies. Shielded thermocouple circuit shorts noise voltage to ground, adapted from Ref 1. For poor pilot flame, you would need to replace the orifice. The thermocouple … Thermocouples are used in many industrial, scientific, and OEM applications. A thermocouple works by taking the difference in voltage between the two junctions, explained by the Seebeck effect. After being Product Manager at WIKA Canada for several years, he transferred to the ETM division covering the Americas region, supporting manufacturing and sales with engineered Electrical Temperature Measurement solutions. … If the thermocouple is broken, the entire system usually won’t start. Solution: The only solution is to periodically replace the thermocouple based on the user’s experience. Unlike many devices, the linearity error is large, over 1% for the common thermocouples, and is even larger below zero degrees. The most common issue is the overheating shutoff sensor, which will cause the unit to shut off, and then back on after it has cooled. A thermocouple should be grounded at only one location. Contamination or particle diffusion can alter your thermocouple's physical makeup and prevent it from conforming to required standards. Loose wires. One of the most common problems with a thermocouple is it becoming dirty and in turn giving off improper readings and closing off the gas supply to your furnace. Watch out : failure to properly seat the thermopile or sensor end of the thermocouple at the gas valve (the end opposite of the flame-tip) into its recess in the gas control can also prevent proper gas heater operation: Fill out the form below and one of our staff will get back to you quickly. Typically, common mode noise is caused by a ground loop that is created when a system has a potential difference between two grounds. The next common issue is problems with the thermocouple. Solution: Make sure no fans or other sources of cooling or heating are located near the reference junction. Simple insulation can also protect the junctions from extreme temperatures. Solution: Doublecheck the connection and, if necessary, swap the thermocouple lead wires. Thermocouples make use of the Seebeck Effect, discovered by Thomas Johann Seebeck in 1821. Gas fireplace troubleshooting problems could be solved with these tips and tricks. by：JVTIA 2020-11-10. This coloration is ANSI standard for thermocouples, but it is not what most people expect. 3.The measurement error occurs when the positive and negative polarity of the thermocouple compensating wire is connected reversely. Sudden loss of heat. Phone: (904) 829-8898 Type R, S, and B thermocouples are “Noble Metal” thermocouples, which are used in high temperature applications (see thermocouple temperature ranges (linked) for details). Traditionally the reference junction was held at 0 °C by an ice bath, as shown in Figure. Like many types of sensors, thermocouples can struggle with a common problem: the issue of acquiring accurate data. Because the tip of a thermocouple is a Common mode noise creates an unwanted voltage that is present on both leads of the thermocouple. Solution: Ground either the transmitter (connection head) or the controller/recorder, but not both. If it is grounded at more than one location, a “ground loop” can be created with current flowing through the thermocouple from one ground to the other. Thermocouples measure temperature differentials, not absolute temperatures. The good news is that a Jacksonville, FL heating repair company is standing by to help you with common thermocouple problems. Reference junction compensation is a necessary part of any precision thermocouple circuit, due to the inescapable fact of the reference junction’s existence. There are two methods: look up the temperat… AVOID BNC CABLES BNC cables and Coaxial cables often have a gold plated center conductor and a copper or nickel outer conductor. The metals used in a thermocouple must have thermoelectric properties. Less Common Thermocouple Problems. A common problem of pressure thermocouple sensor. Six Common Causes for Thermocouple Temperature Measurement Errors, FAQs About Thermocouple Selection: Grounded vs. Ungrounded, Five Things to Take into Account When Measuring Temperature with Thermocouples, Understanding the Latest Technology in Industrial Temperature Measurement. Thermocouples are robust temperature measurement devices that are accurate enough for many industrial and scientific applications. As for insulators, beryllia and thoria are generally recommended, although again problems can occur at the upper end of the temperature spectrum, with wires and insulators potentially reacting. At the other end, the wires are connected to a body of a known temperature, called the reference junction. Reference During routine furnace maintenance, a certified HVAC tech will check, clean or even replace your thermocouple if it is needed. The problem is understandable because red is the usual color for positive charges, whereas the red wire in thermocouple cables typically contains the negative signal. The measured voltage is converted into a temperature unit, with the temperature reading displayed on a device or transmitted to a remote location. While connecting the thermocouple, there might be certain degree of wear on the insulation layer at the outlet of the thermocouple junction box or at other parts of the compensating wire. Problems of Reference Junction Compensation : Thermocouples. This becomes a measurement problem if there is a These wires are manufactured at the highest tolerances to ensure the fewest possible impurities and the greatest consistency in alloy ratio. View Map of Service Areas, 3370 Agricultural Center Drive Relatively inexpensive compared to other temperature measurement technologies, thermocouples are valued for their ability to measure a wide temperature range: from –200° to +1250°C (–328° to +2282°F). This can happen if you have a weak gas control magnet or if the thermocouple needs to be replaced. Thermostat Malfunction – A defective thermostat can lead to problems with the fan or comfort levels in the house. The B type is not usable near or below room temperature because of this. While thermocouples are reliable temperature measurement devices, they do drift with time. The voltage generated by a thermocouple is a function of the temperature difference between the measurement and reference junctions.. Tag : common thermocouple problems. One of the most common problems with Atwood RV water heater is a pilot outage. Troubleshooting things like this can be extremely frustrating. Before you can actually diagnose and identify that the problem has something to do with the thermocouple, you have to know where it is located. NO Heat – A furnace that doesn’t perform its main task may have problems with the thermostat setting, power, gas, or the pilot. Another difficulty with thermocouples is that the voltage does not change linearly with temperature. Loop isolators are also available and can be put in the loop wiring circuit to prevent this from happening. Do you have problems with water heater installation? This is the phenomenon whereby electrical current flows in a circuit made from dissimilar metals, when their two junctions are at different temperatures. 2.The insulation layer of the thermocouple compensating wire is damaged. The reason for the lights going out could be due to clogged air intake vents. Sign up for our newsletter to receive exclusive offers and promotions! This common gas fireplace problem can be a source of panic for homeowners – the combination of a gas appliance and a strange odor can be terrifying! This issue is related to thermocouple issues. As a result, the temperature display value on the display instrument or in the DCS system is generally smaller than usual. It is best to call in a professional technician or plumber if you fail to remedy the problem. The WIKA news subscription informs you, free of charge, by e-mail whenever there is a new blog article. Because a thermocouple measures temperature differentials, any temperature fluctuations around the reference junction (cold junction), which has the known temperature, result in an erroneous temperature reading. 1. Above 1,800°C, however, there can be problems with rhenium vaporization. Jacksonville, FL 32258, Monday – Friday: 8am-5pm As the alloy percentages vary a tiny bit during each manufacturing process, some error in thermocouple accuracy is unavoidable. 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