Thermocouple Data Acquisition from Measurement Computing
A thermocouple also called thermal junctions,
thermoelectric thermometers, or thermal is a temperature-measuring device
consisting of two wires of different metals joined at each end. One junction is
placed where the temperature is to be measured, and the other is kept at a
constant lower temperature. A measuring instrument is connected in the circuit.
The temperature difference causes the development of an electromotive force
(known as the Seebeck effect).
Generally speaking, a thermocouple is the most popular
temperature-sensing device. They can measure a wide range of temperatures.
How they work
Discovered by accident in 1822 by an Estonian physician named Thomas Seebeck,
the term thermocouple originates from the junction between two metals
generating a voltage, which is a function of temperature. This is also known as
Seebeck effect. Although almost any two types of metal can be used to make a
thermocouple, a number of standard types are used because they possess
predictable output voltages and large temperature gradients.
There are many types of thermocouples, but the most popular thermocouple is the K
type, described below:
Typically, a voltage is produced by a thermocouple at any given temperature. For
example, the K type thermocouple at 300°C will produce 12.2mV. This amount
is not measurable by a voltmeter, because the connection of the voltmeter leads
will make a second, undesired thermocouple junction. To accurately measure this
voltage, we must compensate for using any contact made to a thermocouple -- a
technique called cold junction compensation (CJC). In case you are wondering
why connecting a voltmeter to a thermocouple does not make several additional
thermocouple junctions (leads connecting to the thermocouple, leads to the
meter, inside the meter etc), the law of intermediate metals states that a
third metal, inserted between the two dissimilar metals of a thermocouple
junction will have no effect provided that the two junctions are at the same
temperature. It is important to keep this in mind when we construct
thermocouple junctions. Based on this law, it is quite acceptable to make a
thermocouple junction by soldering the two metals together as the solder will
not affect the reading. In practice, however, thermocouple junctions are made
by welding the two metals together (usually by capacitive
discharge) because this ensures that the performance is not limited by the
melting point of solder.
Measurement Computing Corporation offers the largest selection of PC-based data
acquisition and measurement products. Shop our online catalog by selecting a
category above. From PCI, USB, Ethernet, PC/104, ISA, and PCMCIA bus to RS-232, RS-422,
RS-485, and GPIB interfaces; Measurement Computing has everything you need for
your PC-based data acquisition and control applications.
Features
- 8 thermocouple input channels
- Supports J, K, R, S, T, N, E, & B type TCs
- Built-in ambient temperature sensor
- 8 digital I/O bits
General Description
The Advantage of easy temperature measurement! The USB-TC provides 8 inputs and supports all of the common thermocouples. The USB-TC performs all linearization and cold-junction compensation and returns data in degrees C or F.
Powerful, accurate, great value: The internal measurement electronics accuracy exceeds the accuracy specifications of the temperature sensors so you are guaranteed to record the most accurate data possible. Unlike NI who advertises the internal resolution of the A/D converter, MCC guarantees you that the USB-TC will provide the best measurement your sensor is capable of. The USB-TC is the best value in thermocouple measurement at only $37 per channel!
Key Features
- 4 sensor types:
- Thermocouples J, K, R, S, T, N, E, and B
- RTDs (2-, 3- or 4-wire)
- Thermistors
- Semiconductor temperature sensors
- 8 temperature input channels (4 three-wire RTD)
- Built-in ambient temperature sensor
- Independent temp inputs
- 8 digital I/O bits
General Description
The Advantage of easy, flexible temperature measurement! the USB-TEMP provides 8 temperature inputs and supports all of the common sensors types-thermocouples, RTDs, thermistors and semiconductor temperature sensors. Each channel can monitor any of the supported input types allowing you to mix and match the sensor to measurement without needing additional signal conditioning. No other product on the market gives you these kinds of Advantages.
Powerful, accurate, great value: The internal measurement electronics accuracy exceeds the accuracy specifications of the temperature sensors so you are guaranteed to record the most accurate data possible. Unlike NI, who advertises the internal resolution of the A/D converter, MCC guarantees you that the USB-TEMP will provide the best measurement your sensor is capable of. Compared to any other PCI- or USB-based product, the USB-TEMP is an amazing value: other temperature measurement products that support multiple sensor types cost at least $500 more.
PCI-DAS-TC $599
Key Features
- 16 Differential thermocouple input channels plus one CJC channel
- Four programmable gain ranges
- Reads thermocouple types J, K, E, T, R, S, B
- Conversion to degrees C or degrees F
- Gain and Offset automatically calibrated on each scan
- Cold Junction Compensation done on each scan
- Overall Conversion rate 4.6 to 22.2 ms
- Provides 500 VDC isolation
Thermocouple Boards
Thermocouple USB
Ethernet Thermocouple
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