Questions tagged [thermocouple]

A thermocouple is formed by a contact of two (2) dissimilar conductors. The voltage across thermocouple is governed by Seebeck effect. Thermocouples are widely used as temperature sensors.

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Can a thermocouple be encased in a custom stainless steel tube?

I would like to read the temperature of oil in a metallic vessel. However I'd like to route the thermocouple so it stays out of the way. Is it OK to just insert the "naked" thermocouple &...
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Temperature circuit not functioning

I am attempting to help mentor some high school kids on circuits and obviously not doing a very good job. We are trying to get a prototype PCB working that uses a max31856mud datasheet and k ...
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Landing a Thermocouple on a surface with voltage present

I am connecting multiple K-type TCs (thermocouples) to an electric engine prototype. I have had a problem with the TCs having up to 150 volts on them when the engine is running. I don't know the ...
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Thermocouple IC MAX31856 circuit what is DRDY

I have a prototype board that seems to only output non-sensible values for K thermocouple readings, with no response to actual temperature changes. Prior to this a breakout board with this exact IC ...
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Furnace circuit ideas: constant temperature with thermocouple & heating element

I am wanting to make what we will just call a furnace that will always operate near 1800°F. I'm looking for circuit ideas or a direction in order to maintain the temperature of the furnace. The ...
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Thermocouple bias with LTC2053

This LTC2053 application note shows a thermocouple bias using two 10 MΩ and two 1 MΩ resistors. I understand the idea that the power supply is divided by two 10 MΩ resistors for good common mode ...
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Thermocouple K Type using a jack plug instead of the normal connector

I have a few thermocouple K Type using the classic two lead connector. I would like to change that connector to a male jack type like this: So I can connect it to the female connector that has ...
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Relay Module with Arduino Uno and K-Type Thermocouple

I am working on a project for school. The goal is to use thermocouples to measure temperatures. The measured temp will control whether or not the lightbulb is turned on. The components used will be an ...
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Thermocouple conductor direct current resistance

Does a thermocouple conductor have a direct current resistance requirement?
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Thermocouple wire diameter

I have four possible scenarios for making a type T thermocouple: use a 24AWG copper wire and a 24AWG constantan wire use a 20AWG copper wire and a 20 AWG constantan wire use a 24AWG copper wire and a ...
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Output voltage at different output optical chopper frequencies

I have a circuit as shown in the figure and I am using it to extract output voltage of thermopile (to determine the time constant of thermopile ) at different output frequencies. The optical chopper ...
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Is it ok to solder thermocouple wire ends?

I am using T type thermocouple wire. I am using it in a situation where I don't want the sensor to fail hence I thought it is a good idea to solder the ends together instead of only twisting them to ...
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Using plain connectors on thermocouple / external cold junction compensation

We'd like to use plain automotive connectors to connect our thermocouples. What we are looking for is the ruggedness and economy of such connectors. Of course, that brings the problem of material ...
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Thermocouple wire extension

I want to use a thermocouple (K type) for a PID temperature controller in a heating system. The thermocouple should be pluggable to the system. I decided to use an industrial grade connector like ...
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Making Thermocouples With Only One Type of Wire

Can thermocouples be made with only one type of wire? I wonder if a thermocouple would work if I use two 10-cm copper wires given that their diameters are vastly different. I know that the two copper ...
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Temperature gradients and different types of wires in thermocouples

I use long (10-m) copper-constantan thermocouples for work to measure temperature. The temperature gradient is only present in the 15 cm nearest the hot junction; the remaining 9.85 m of these ...
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MAX6675 k-type thermocouple ADC is giving high readings

I have designed and built a small fairly simple circuit that uses a MAX6675 chip to take temperature readings from a multiplexed array of 16 k-type thermocouples. Datasheets: MAX6675: https://www....
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Using Thermal Epoxy vs Super Glue for Thermal Couple temperature measuring

Which practice is better for measuring the temperature if a MCU on a PCB with a thermocouple: Measuring on the case of the MCU with thermal epoxy attached to the thermal couple, or super glue? I feel ...
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Confused about MAX6675 thermocouple sensor SPI protocol

I'm using an AVR microcontroller to take readings from a MAX6675 (SPI K-type thermocouple ADC chip). I am having difficulty understanding what is required by this chip's SPI interface. The datasheet (...
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K thermocouple readings bad probe or circuit?

I recently put together this circuit to read a K thermocouple. It takes the probes reading and converts it into an analog voltage. The design came from: I am getting poor readings from the circuit ...
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How to measure the temperature of a surface using an Arduino?

I'd like to measure the surface temperature of of a metal surface, to see how much that metal surface is heating up. I'm trying to recreate The EngineGuard. The EngineGuard uses a 10mm washer, that ...
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1 vote
1 answer
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Why is this thermocouple amplifier with analog output circuit not working?

I am trying to assemble a circuit based on this datasheet: The schematic I derived from the circuit is: This was made into a PCB footprint The readings I am getting from this circuit are much too ...
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What is the difference in power consumption between thermocouple and thermistor?

I am working on a project to transmit sensor data and I chose to go with a temperature sensor to connect to a micro-controller. Since I care a lot about power consumption for my project, I would like ...
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Variation of neutral temperature in a thermocouple

Neutral temperature =-(a÷b), where a and b are constant for metals A and B, but the inversion temperature = -2(a÷b), but inversion temperature depends upon the cold juction so why is the neutral ...
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4 votes
2 answers
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Best way to get measurements from 16 K-type thermocouples with an MCU?

I'm working on a project, which is focused on taking frequent (250ms interval or smaller) measurements of extreme temperatures (0-700 C) in 16 points. I need to take measurements of multiple ...
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My soldering station's iron is rated for 70W, can I modify a 75W one to work with it?

I have an Aoyue 936A soldering iron rated at 24V/70 watts. I came across a cheapo soldering iron rated at 24V/75W and rewired it according to the pinouts of the original one. The thermocouple readings ...
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MAX 6675 K-type unstable to say the least

have two breakout boards with MAX6675. I have 3 different K-type thermo elements. The MAX is connected to an AVR (atmega8) for communication, driver my own, communicates to PC on UART. Now none of the ...
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Need to identify faulty thermistor in order to find a like or better replacement

I have an ic with a poorly performing thermistor I'd like to replace with a more accurate, more sensitive component. The first step is finding out what thermistor I likely have or at least who made it....
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Cold-junction point

I'm converting an kitchen top oven into a reflow oven and all seems fine except for the temperature measurements. Using the same K-type thermocouple, but an external cold junction, the measurements ...
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Noise equivalent power of thermopile sensor?

I am working on the characterisation of thermopile sensor and stuck in determining the NEP of the sensor. My thermopile sensor with AD8630 amplifier receives IR radiation coming from the blackbody at ...
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Understanding thermocouple transmitter wiring

I'm trying to use the RMTJ40BD thermocouple (page 12) and I'm having trouble understanding the wiring diagram for the output. The manual says that Vo and OPG are the outputs but what is OPG, what ...
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How are analog thermocouple meters calibrated?

In most modern thermocouple measuring equipment, the input is high impedance and approximates a perfect voltmeter. This makes the thermocouple measurement easy because there is no current flowing ...
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Thermocouple troubleshooting

I have a system error pop-up on an HMI of one of my machines. Since it only had a number, I tried to reach the manufacturer for the error code description. They said that this error usually is the ...
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Thermocouple simulator circuit : isolation & voltage reference

I'm designing a multi-channel (6-10) thermocouple simulator. For different reasons, all the outputs must be isolated to simulate completely the behaviour of the real-life thermocouple. To do the task ...
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1 answer
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How to amplify a thermocouple that shares a wire with a heating element (soldering iron?)

I have a problem that I can't seem to wrap my head around. I am designing a controller for a JBC handpiece, but the cartridgess are only three pins (JBC Nano only two.) I'm trying to design a ...
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1 vote
1 answer
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Max31855k - fluctuation and drift

I'm using a b 31855k breakout board (a chinese one at that) with the olimex A20 and a K-type thermocouple (which works OK on another device with the 31855k). The problem is, that the thermocouple temp ...
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Thermocouple comparator choose

I measured the parameters of a thermocouple (R1). R1in=5 Ohm, V=1..10 mV (measured by multimetr). Ipositive = 5v/20000 = 0,25mА, and Upositive max = 0,25 * 0,001 * 100 = 25mV I have lm339, lm324. ...
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How to keep heat away from an electronics enclosure?

I’m converting a simple cooking hot plate to have it’s temperature controlled by an arduino, with an lcd. It’s metallic casing gets really hot when the plate is turned on. As I’ll remove the original ...
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4 answers
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Building a furnace with more than one thermocouple for accurate temperature measurement

I am a mechanical engineering student. I am in the process of making a special purpose heating equipment. It could be considered as a 3 phase electrical resistance furnace. I want the temperature in ...
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1 answer
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How to measure extremely high temperatures?

I'm interested in building or buying an electric (arc or induction) furnace for smelting & heat-treating metals. Most designs I've seen utilize PID controllers and thermocouples. How are extreme ...
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8 votes
3 answers
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Effect of length on a thermocouple's accuracy

I'm a mechanical engineer working on acquiring some temperature data using thermocouples. Q. I wanted to know the effect of wire length on a thermocouple's accuracy. I don't have much of electrical ...
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Thermopile temperature sensor

I am using an MRT511 thermopile temperature sensor and COS77DT for amplifying the temperature sensor output. I used Recommended circuit in the MRT511 datasheet but output voltage of the op-amp not ...
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2 outputs of same op amp gives different voltages

I am using lm358p op-amp for 2 different heaters I connected both of them in a single op-amp and it didn't work firstly I thought that the problem was thermocouples I swapped them but the problem kept ...
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3 answers
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How to access a Thermocouple signal in PC?

I'm looking for the way to access a thermocouple signal to use it in my own software. I suppose that I have to place a data acquisition system (something like this https://www.dataq.com/data-...
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Thermocouple amplifier and cold junction compensation

I am trying to design a thermocouple amplifier with cold junction compensation. I already designed a simple amplifier for the thermocouple using LM358. Note that I can built this entire circuit using ...
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Thermocouple Equivalent Circuit

I am about to design an amplifier to J | K Thermocouples, but I have been unable to find a trustable equivalent circuit|model|specs for them. I know a J Type Thermocouple has some general specs, such ...
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Regulating precision heating

Whats the simplest electr(on)ic(al) method for heating a coil or similar element to a specific temperature? Generating heat is easy; dictating and regulating a specific temperature is the hard part. ...
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2 votes
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Mux switching one leg of differential signal

I found the schematic below for a muxed thermocouple circuit from this web page. This circuit uses a mux to switch just one leg of the thermocouples. While I am sure that this works fine I have a ...
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Voltage of thermocouple

As we know, when we use a thermocouple, we measure mV value. This is what I wonder. Why we measure voltage not current? Like voltage, I think the current of T/C is proportional to temperature too.
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Splitting/y'ing a thermocouple amongst 2+ inputs

The system in question has just one type K thermocouple. Is it a bad practice to Y a thermocouple into 2+ thermocouple inputs? For example, Y a thermocouple into: DAC thermocouple input card Limit ...
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