Thermocouple Primer - Revision history

Mparadis: /* Things to Watch For */

2015-01-22T20:00:36Z

Things to Watch For

← Older revision		Revision as of 20:00, 22 January 2015
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	More information about how to avoid ground loops in thermocouples can be found [http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ here, on the Phidgets blog].		More information about how to avoid ground loops in thermocouples can be found [http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ here, on the Phidgets blog].

			===Polarity===
			Each thermocouple has a positive and a negative lead. If you hook it up with the reverse polarity, you will experience unpredictable readings and incorrect temperatures. Always make sure proper polarity is maintained at each junction and connector along your thermocouple.

	===Interference===		===Interference===

Mparadis: /* Exposed */

2014-06-02T16:54:06Z

Exposed

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	* Limited to non-corrosive, non-pressurized applications.		* Limited to non-corrosive, non-pressurized applications.
	* The thermocouple has no protection from physical contact.		* The thermocouple has no protection from physical contact.

	~~For more information on thermocouple grounding, have a look at [http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ this blog post].~~

	==Things to Watch For==		==Things to Watch For==

Mparadis: /* Exposed */

2014-06-02T16:53:40Z

Exposed

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	* The thermocouple has no protection from physical contact.		* The thermocouple has no protection from physical contact.

	For more information on thermocouple grounding, have a look at [[http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ this blog post]].		For more information on thermocouple grounding, have a look at [http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ this blog post].

	==Things to Watch For==		==Things to Watch For==

Mparadis: /* Junction Type */

2014-06-02T16:53:12Z

Junction Type

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	[[File:Thermocouple.jpg\|350px\|thumb\|link=\|'''Junction Types'''<br/>A cross-sectional view of the three most common junction types.<br/>[[Media:Thermocouple.jpg\|Full-sized Image]]]]		[[File:Thermocouple.jpg\|350px\|thumb\|link=\|'''Junction Types'''<br/>A cross-sectional view of the three most common junction types.<br/>[[Media:Thermocouple.jpg\|Full-sized Image]]]]

	An important feature to consider when choosing a thermocouple is the junction type. This describes the degree to which the sensing end of the thermocouple is exposed to the environment it's measuring. There are three main types of junctions: Grounded, Ungrounded, and Exposed.		An important feature to consider when choosing a thermocouple is the junction type. This describes the degree to which the sensing end of the thermocouple is exposed to the environment it's measuring. There are three main types of junctions: Grounded, Ungrounded, and Exposed.

	====Ungrounded====		====Ungrounded====
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	* Limited to non-corrosive, non-pressurized applications.		* Limited to non-corrosive, non-pressurized applications.
	* The thermocouple has no protection from physical contact.		* The thermocouple has no protection from physical contact.

			For more information on thermocouple grounding, have a look at [[http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ this blog post]].

	==Things to Watch For==		==Things to Watch For==

Kat at 16:28, 2 June 2014

2014-06-02T16:28:31Z

← Older revision		Revision as of 16:28, 2 June 2014
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	==Things to Watch For==		==Things to Watch For==
			===Grounding===
			A “ground loop” happens when two points in a circuit are at different potentials, when they are expected to be the same. This difference in electrical potentials causes a build up of static electricity that can give electrical shocks to people and electronics. In the case of thermocouples and thermocouple boards, the negative terminal on the 1051 1-input thermocouple boards is USB ground, as is the ground terminal on the 1048 4-input board. So, if you ground the junction of your thermocouple when using these boards and the material it’s affixed to has a different voltage than the ground on the computer, you’ve created a circuit with two points at different potentials.

			More information about how to avoid ground loops in thermocouples can be found [http://phidgets.wordpress.com/2014/06/02/how-to-avoid-grounding-a-thermocouple/ here, on the Phidgets blog].

	===Interference===		===Interference===
	When measuring from a thermocouple, each thermocouple is compared to adapter's internal ground. If your thermocouple is measuring a conductive device which cannot equalize to the ground of the adapter, you should isolate the thermocouple wire using thermally conductive epoxy. Thermocouples are conductive, and are very good at shorting electrical systems together. If in doubt, do not allow the thermocouple wire to contact other metal parts.		When measuring from a thermocouple, each thermocouple is compared to adapter's internal ground. If your thermocouple is measuring a conductive device which cannot equalize to the ground of the adapter, you should isolate the thermocouple wire using thermally conductive epoxy. Thermocouples are conductive, and are very good at shorting electrical systems together. If in doubt, do not allow the thermocouple wire to contact other metal parts.

Burley: /* Wire Length */

2013-01-22T19:40:44Z

Wire Length

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	Since a thermocouple works due to the interaction at the junction of two different metals, it isn't advisable attach two pieces of thermocouple wire simply by soldering them- This would create an additional junction that would interfere with the measurement signal. The best way to connect two thermocouple wires is to buy a connector of the same letter type that clamps onto either end, such as [http://www.omega.com/pptst/SMPW-CC.html this K-type connector] from Omega.		Since a thermocouple works due to the interaction at the junction of two different metals, it isn't advisable attach two pieces of thermocouple wire simply by soldering them- This would create an additional junction that would interfere with the measurement signal. The best way to connect two thermocouple wires is to buy a connector of the same letter type that clamps onto either end, such as [http://www.omega.com/pptst/SMPW-CC.html this K-type connector] from Omega.

			On the flip side, you can cut thermocouples down to a shorter length if you require that as well. Just make sure to cut the size you want out of the side with the actual sensing area on it. The junction between the 2 metals is what allows the device to measure temperature so you need to have the end with the junction on the length you will be using or the thermocouple won't do anything.

	==How to connect your Thermocouple==		==How to connect your Thermocouple==

Mparadis: /* Wire Length */

2012-10-03T16:03:47Z

Wire Length

← Older revision		Revision as of 16:03, 3 October 2012
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	===Wire Length===		===Wire Length===
	Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [[Addressing_Electromagnetic_Interference_with_Phidgets\|Addressing EMI issues]].		Very long thermocouples are okay (even 100m), but if there are measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [[Addressing_Electromagnetic_Interference_with_Phidgets\|Addressing EMI issues]] for more information.

	Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire, not generic wire.		Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire of the same letter type, not just generic wire. Often, thermocouple extension wire will be rated for a narrower temperature range, since it isn't intended to be used in the sensing end of the application.

			Since a thermocouple works due to the interaction at the junction of two different metals, it isn't advisable attach two pieces of thermocouple wire simply by soldering them- This would create an additional junction that would interfere with the measurement signal. The best way to connect two thermocouple wires is to buy a connector of the same letter type that clamps onto either end, such as [http://www.omega.com/pptst/SMPW-CC.html this K-type connector] from Omega.

	==How to connect your Thermocouple==		==How to connect your Thermocouple==

Mparadis: /* Wire Length */

2012-10-03T14:39:32Z

Wire Length

← Older revision		Revision as of 14:39, 3 October 2012
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	Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [[Addressing_Electromagnetic_Interference_with_Phidgets\|Addressing EMI issues]].		Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [[Addressing_Electromagnetic_Interference_with_Phidgets\|Addressing EMI issues]].

	Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire not generic wire.		Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire, not generic wire.

	==How to connect your Thermocouple==		==How to connect your Thermocouple==

Mparadis: /* Things to Watch For */

2012-10-03T14:39:03Z

Things to Watch For

← Older revision		Revision as of 14:39, 3 October 2012
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	===Wire Length===		===Wire Length===
	Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [~~http://www.phidgets.com/documentation/Tutorials/Addressing_EMI_Issues_Tutorial.pdf~~ Addressing EMI issues].		Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [[Addressing_Electromagnetic_Interference_with_Phidgets\|Addressing EMI issues]].

	Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire not generic wire.		Note that thermocouples use special wires. This means that if you want to extend the length of your thermocouple you need to use thermocouple wire not generic wire.

Mparadis: /* Wire Size */

2012-10-03T14:36:54Z

Wire Size

← Older revision		Revision as of 14:36, 3 October 2012
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	thermocouple wire. That is, a very thin thermocouple may not reach the full temperature range. On the other hand, a thinner thermocouple does reduce the amount of thermal distortion introduced.		thermocouple wire. That is, a very thin thermocouple may not reach the full temperature range. On the other hand, a thinner thermocouple does reduce the amount of thermal distortion introduced.

	Selecting the wire ~~size~~ used in the thermocouple sensor depends upon your application. Generally, when longer life is required for the higher temperatures, the larger size ~~wires~~ should be chosen. When sensitivity is the prime concern, the smaller sizes should be used.		Selecting the wire gauge used in the thermocouple sensor depends upon your application. Generally, when longer life is required for the higher temperatures, the larger size gauges should be chosen. When sensitivity is the prime concern, the smaller sizes should be used.

	===Wire Length===		===Wire Length===
	Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [http://www.phidgets.com/documentation/Tutorials/Addressing_EMI_Issues_Tutorial.pdf Addressing EMI issues].		Very long thermocouples are okay (even 100m), but if there is measurement stability issues or USB resets, ferrite beads can be added to the thermocouple wire close to the adapter. See our tutorial on [http://www.phidgets.com/documentation/Tutorials/Addressing_EMI_Issues_Tutorial.pdf Addressing EMI issues].