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bbradburry(at)bellsouth.n
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 Posted: Mon Aug 27, 2012 6:16 am Post subject: Meter for reading Millivolts |
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I think I have a bad EGT thermocouple and I have been trying to test it.
One of my EGTs seems ok and the other is really low in temperature reading.
When I test the two thermocouples I get either no readings or really high
readings that go down when I heat the thermocouple.
I bought a new VOM tester that had a temp probe as part of it to try and
test the probes. But even with this tester I get nonsense readings.
For example, if I plug the probe that came with the meter into the temp
slot, it gives believable temp readings, but if I unplug the probe and try
to read the output of the probe using the test leads and the 200MV scale, I
get a reading of zero.
I bought a new probe for the engine, but when I test either the new probe or
the old (bad?) one with the test leads and the 200MV scale, I get the same
results as above.
I need to buy a meter that will read reliably on the MV scale. What meter
do you suggest and where can I get one that is not too expensive?
Bill B
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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harley(at)AgelessWings.co
Guest
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| Posted: Mon Aug 27, 2012 6:29 am Post subject: Meter for reading Millivolts |
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Bill...
I use this one to test my EGT and CHT thermocouples...it also has a light meter, and a temp sensor built in...I replaced my old B&K (that I had for years before it finally bit the dust) with it, and it's every bit as good...
It also measures sound levels...but I haven't really tested that function yet.
www.harborfreight.com/5-in-1-digital-multimeter-98674.html
They currently have a 20% off coupon here as well that's good online or in the store:
http://tinyurl.com/9uf4wfw
Harley
On 8/27/2012 10:14 AM, Bill Bradburry wrote:
[quote] | Quote: | --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net> (bbradburry(at)bellsouth.net)
I think I have a bad EGT thermocouple and I have been trying to test it.
One of my EGTs seems ok and the other is really low in temperature reading.
When I test the two thermocouples I get either no readings or really high
readings that go down when I heat the thermocouple.
I bought a new VOM tester that had a temp probe as part of it to try and
test the probes. But even with this tester I get nonsense readings.
For example, if I plug the probe that came with the meter into the temp
slot, it gives believable temp readings, but if I unplug the probe and try
to read the output of the probe using the test leads and the 200MV scale, I
get a reading of zero.
I bought a new probe for the engine, but when I test either the new probe or
the old (bad?) one with the test leads and the 200MV scale, I get the same
results as above.
I need to buy a meter that will read reliably on the MV scale. What meter
do you suggest and where can I get one that is not too expensive?
Bill B
-----
No virus found in this message.
Checked by AVG - www.avg.com
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[b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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bbradburry(at)bellsouth.n
Guest
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| Posted: Mon Aug 27, 2012 9:39 am Post subject: Meter for reading Millivolts |
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Harley,
I didn’t see that one in the store. They had this one
http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html
This is the one I bought and with it I get the nonsense readings that I describe in my previous msg. I wonder is there a trick to the testing to get accurate readings?
Bill
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Harley
Sent: Monday, August 27, 2012 10:29 AM
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Meter for reading Millivolts
Bill...
I use this one to test my EGT and CHT thermocouples...it also has a light meter, and a temp sensor built in...I replaced my old B&K (that I had for years before it finally bit the dust) with it, and it's every bit as good...
It also measures sound levels...but I haven't really tested that function yet.
www.harborfreight.com/5-in-1-digital-multimeter-98674.html
They currently have a 20% off coupon here as well that's good online or in the store:
http://tinyurl.com/9uf4wfw
Harley
On 8/27/2012 10:14 AM, Bill Bradburry wrote:
| Quote: | | Quote: | | --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net> I think I have a bad EGT thermocouple and I have been trying to test it.One of my EGTs seems ok and the other is really low in temperature reading.When I test the two thermocouples I get either no readings or really highreadings that go down when I heat the thermocouple. I bought a new VOM tester that had a temp probe as part of it to try andtest the probes. But even with this tester I get nonsense readings.For example, if I plug the probe that came with the meter into the temp |
0123456789 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
0 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
1 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
2 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
3 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
4 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
5 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
6 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
7 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
8 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
9 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
0 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
1 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
2 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
3 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
4 |
| Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
5 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
6 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
7 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
8 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
9 | Quote: | | When I test the two thermocouples I get either no readings or really high |
0 | Quote: | | When I test the two thermocouples I get either no readings or really high |
1 | Quote: | | When I test the two thermocouples I get either no readings or really high |
2 | Quote: | | When I test the two thermocouples I get either no readings or really high |
3 | Quote: | | When I test the two thermocouples I get either no readings or really high |
4 | Quote: | | When I test the two thermocouples I get either no readings or really high |
5 | Quote: | | When I test the two thermocouples I get either no readings or really high |
6 | Quote: | | When I test the two thermocouples I get either no readings or really high |
7 | Quote: | | When I test the two thermocouples I get either no readings or really high |
8 | Quote: | | When I test the two thermocouples I get either no readings or really high |
9 | Quote: | | readings that go down when I heat the thermocouple. |
0 | Quote: | | readings that go down when I heat the thermocouple. |
1 | Quote: | | readings that go down when I heat the thermocouple. |
2 | Quote: | | readings that go down when I heat the thermocouple. |
3 | Quote: | | readings that go down when I heat the thermocouple. |
4
[quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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harley(at)agelesswings.co
Guest
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| Posted: Mon Aug 27, 2012 9:46 am Post subject: Meter for reading Millivolts |
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|
I'm not familiar with that one, but looking at the picture, I see an input for K thermocouples...if you plug your thermocouple into those you should get an actual temperature reading (in centigrade, it seems). Maybe you are having a problem when you try to read them as millivolts using the probes on the meter instead? Even the J thermocouples will work in the K thermocouple input, just be a little bit off.
Harley
On 8/27/2012 1:36 PM, Bill Bradburry wrote:
[quote] v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} <![endif]--> st1\:*{behavior:url(#default#ieooui) } <![endif]--> <![endif]--> <![endif]-->
Harley,
I didn’t see that one in the store. They had this one
http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html
This is the one I bought and with it I get the nonsense readings that I describe in my previous msg. I wonder is there a trick to the testing to get accurate readings?
Bill
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Harley
Sent: Monday, August 27, 2012 10:29 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: AeroElectric-List: Meter for reading Millivolts
Bill...
I use this one to test my EGT and CHT thermocouples...it also has a light meter, and a temp sensor built in...I replaced my old B&K (that I had for years before it finally bit the dust) with it, and it's every bit as good...
It also measures sound levels...but I haven't really tested that function yet.
www.harborfreight.com/5-in-1-digital-multimeter-98674.html
They currently have a 20% off coupon here as well that's good online or in the store:
http://tinyurl.com/9uf4wfw
Harley
On 8/27/2012 10:14 AM, Bill Bradburry wrote:
| Quote: | | Quote: | | --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net> (bbradburry(at)bellsouth.net) I think I have a bad EGT thermocouple and I have been trying to test it.One of my EGTs seems ok and the other is really low in temperature reading.When I test the two thermocouples I get either no readings or really highreadings that go down when I heat the thermocouple. I bought a new VOM tester that had a temp probe as part of it to try andtest the probes. But even with this tester I get nonsense readings.For example, if I plug the probe that came with the meter into the temp |
0 1 2 3 4 5 6 7 8 9 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
0 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
1 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
2 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
3 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
4 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
5 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
6 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
7 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
8 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
9 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
0 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
1 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
2 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
3 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
4 |
| Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
5 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
6 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
7 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
8 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
9 | Quote: | | When I test the two thermocouples I get either no readings or really high |
0 | Quote: | | When I test the two thermocouples I get either no readings or really high |
1 | Quote: | | When I test the two thermocouples I get either no readings or really high |
2 | Quote: | | When I test the two thermocouples I get either no readings or really high |
3 | Quote: | | When I test the two thermocouples I get either no readings or really high |
4 | Quote: | | When I test the two thermocouples I get either no readings or really high |
5 | Quote: | | When I test the two thermocouples I get either no readings or really high |
6 | Quote: | | When I test the two thermocouples I get either no readings or really high |
7
| Quote: | | When I test the two thermocouples I get either no readings or really high |
8
No virus found in this message.
Checked by AVG - www.avg.com
Date: 08/27/12 [b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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harley(at)AgelessWings.co
Guest
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| Posted: Mon Aug 27, 2012 10:02 am Post subject: Meter for reading Millivolts |
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|
I just looked up the millivolt readings for a type K thermocouple
at room temperature (20 c). And the problem you may be having is
trying to read that with the 200 millivolt scale. It is only
about 0.8mv! As long as plugging into the thermocouple slot
gives you a reading near the proper temperature, the thermocouple
is working...I never tried to read them on a millivolt scale as
I've always had actual instruments around that could read them
and have the tables built in to convert to the proper
temperatures...like those two meters we've been talking about.
Harley
-----------------------------------------------------------------
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bbradburry(at)bellsouth.n
Guest
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| Posted: Mon Aug 27, 2012 10:05 am Post subject: Meter for reading Millivolts |
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|
They read Zero with the probes and the thermocouples have ring terminals on
them so they will not fit into the sockets on the meter for the thermocouple
plug.
I need to be able to read them with the probes because I need to check the
outputs behind the panel just before the connection to the engine monitor so
I know that the wires are good all the way to the monitor. That way I will
know what the monitor is reading. And I will know where the problem is
located in case of an error in the temp reading.
Bill
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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bbradburry(at)bellsouth.n
Guest
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| Posted: Mon Aug 27, 2012 10:13 am Post subject: Meter for reading Millivolts |
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|
I put the thermocouples on a lit 60W light bulb for about 5 minutes to test that low reading theory. It didn’t seem to make any difference to the meter. I thought buying one with the K probe would ensure that it would read on the millivolt scale, but it seems that didn’t work. It appears to read plugged into the K probe socket, but not with the probes on the 200 MV scale.
Bill
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Harley
Sent: Monday, August 27, 2012 1:58 PM
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Meter for reading Millivolts
I just looked up the millivolt readings for a type K thermocouple at room temperature (20 c). And the problem you may be having is trying to read that with the 200 millivolt scale. It is only about 0.8mv! As long as plugging into the thermocouple slot gives you a reading near the proper temperature, the thermocouple is working...I never tried to read them on a millivolt scale as I've always had actual instruments around that could read them and have the tables built in to convert to the proper temperatures...like those two meters we've been talking about.
Harley
.
On 8/27/2012 1:36 PM, Bill Bradburry wrote:
[quote]
<![endif]--> <![endif]-->Harley,
I didn’t see that one in the store. They had this one
http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html
This is the one I bought and with it I get the nonsense readings that I describe in my previous msg. I wonder is there a trick to the testing to get accurate readings?
Bill
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Harley
Sent: Monday, August 27, 2012 10:29 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: AeroElectric-List: Meter for reading Millivolts
Bill...
I use this one to test my EGT and CHT thermocouples...it also has a light meter, and a temp sensor built in...I replaced my old B&K (that I had for years before it finally bit the dust) with it, and it's every bit as good...
It also measures sound levels...but I haven't really tested that function yet.
www.harborfreight.com/5-in-1-digital-multimeter-98674.html
They currently have a 20% off coupon here as well that's good online or in the store:
http://tinyurl.com/9uf4wfw
Harley
On 8/27/2012 10:14 AM, Bill Bradburry wrote:
| Quote: | | Quote: | | --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net> I think I have a bad EGT thermocouple and I have been trying to test it.One of my EGTs seems ok and the other is really low in temperature reading.When I test the two thermocouples I get either no readings or really highreadings that go down when I heat the thermocouple. I bought a new VOM tester that had a temp probe as part of it to try andtest the probes. But even with this tester I get nonsense readings.For example, if I plug the probe that came with the meter into the temp |
0123456789 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
0 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
1 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
2 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
3 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
4 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
5 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
6 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
7 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
8 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
9 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
0 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
1 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
2 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
3 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
4 |
| Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
5 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
6 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
7 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
8 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
9 | Quote: | | When I test the two thermocouples I get either no readings or really high |
0 | Quote: | | When I test the two thermocouples I get either no readings or really high |
1 | Quote: | | When I test the two thermocouples I get either no readings or really high |
2 | Quote: | | When I test the two thermocouples I get either no readings or really high |
3[b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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harley(at)agelesswings.co
Guest
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| Posted: Mon Aug 27, 2012 10:22 am Post subject: Meter for reading Millivolts |
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|
Just a continuity check of the wires will do that...if the wires are continuous from the panel to the probe and back (put your probes across the yellow and red wire in any thermocouple pair - with at least one disconnected from the display so that you aren't reading anything inside the display - and you should get a continuous reading) then the thermocouple is working...remember, a thermocouple is nothing more than two dissimilar wires attached at one end.
Harley
On 8/27/2012 2:03 PM, Bill Bradburry wrote:
[quote] v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} <![endif]--> st1\:*{behavior:url(#default#ieooui) } <![endif]--> <![endif]--> <![endif]-->
They read Zero with the probes and the thermocouples have ring terminals on them so they will not fit into the sockets on the meter for the thermocouple plug.
I need to be able to read them with the probes because I need to check the outputs behind the panel just before the connection to the engine monitor so I know that the wires are good all the way to the monitor. That way I will know what the monitor is reading. And I will know where the problem is located in case of an error in the temp reading.
Bill
.
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Harley
Sent: Monday, August 27, 2012 1:44 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: AeroElectric-List: Meter for reading Millivolts
I'm not familiar with that one, but looking at the picture, I see an input for K thermocouples...if you plug your thermocouple into those you should get an actual temperature reading (in centigrade, it seems). Maybe you are having a problem when you try to read them as millivolts using the probes on the meter instead? Even the J thermocouples will work in the K thermocouple input, just be a little bit off.
Harley
On 8/27/2012 1:36 PM, Bill Bradburry wrote:
| Quote: |
<![endif]--> <![endif]-->Harley,
I didn’t see that one in the store. They had this one
http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html
This is the one I bought and with it I get the nonsense readings that I describe in my previous msg. I wonder is there a trick to the testing to get accurate readings?
Bill
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) [mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of Harley
Sent: Monday, August 27, 2012 10:29 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: AeroElectric-List: Meter for reading Millivolts
Bill...
I use this one to test my EGT and CHT thermocouples...it also has a light meter, and a temp sensor built in...I replaced my old B&K (that I had for years before it finally bit the dust) with it, and it's every bit as good...
It also measures sound levels...but I haven't really tested that function yet.
www.harborfreight.com/5-in-1-digital-multimeter-98674.html
They currently have a 20% off coupon here as well that's good online or in the store:
http://tinyurl.com/9uf4wfw
Harley
On 8/27/2012 10:14 AM, Bill Bradburry wrote:
| Quote: | | Quote: | | --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net> (bbradburry(at)bellsouth.net) I think I have a bad EGT thermocouple and I have been trying to test it.One of my EGTs seems ok and the other is really low in temperature reading.When I test the two thermocouples I get either no readings or really highreadings that go down when I heat the thermocouple. I bought a new VOM tester that had a temp probe as part of it to try andtest the probes. But even with this tester I get nonsense readings.For example, if I plug the probe that came with the meter into the temp |
0 1 2 3 4 5 6 7 8 9 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
0 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
1 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
2 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
3 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
4 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
5 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
6 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
7 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
8 | Quote: | | I think I have a bad EGT thermocouple and I have been trying to test it. |
9 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
0 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
1 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
2 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
3 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
4 |
| Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
5 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
6 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
7 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
8 | Quote: | | One of my EGTs seems ok and the other is really low in temperature reading. |
9 When I test the two thermocouples I get either no readings or really high |
0
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Date: 08/27/12 [b]
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nuckolls.bob(at)aeroelect
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| Posted: Mon Aug 27, 2012 4:13 pm Post subject: Meter for reading Millivolts |
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To: aeroelectric-list(at)matronics.com
Subject: Re: Meter for reading Millivolts
At 01:17 PM 8/27/2012, you wrote:
Just a continuity check of the wires will do that...if the wires are continuous from the panel to the probe and back (put your probes across the yellow and red wire in any thermocouple pair - with at least one disconnected from the display so that you aren't reading anything inside the display - and you should get a continuous reading) then the thermocouple is working...remember, a thermocouple is nothing more than two dissimilar wires attached at one end.
Exactly. As a general rule, thermocouples
either work . . . or they don't. If one is
presented with readings from a thermocouple
that appear to be out of calibration, the
source of that error is generally associated
with installation or measurement/display.
I'll refer the readers to this excerpt from
the 'Connection on the topic of thermocouples.
http://tinyurl.com/94uk94t
. . . in particular, take a peek at Table
14-2 where we see that the USEFUL values
of voltage being measured are TINY. The
delta-voltage is less than 10 millivolts
for a Type-K thermocouple looking at a
cylinder head temperature of 425F. That span
needs to be sliced up into say 42 parts
to discern the difference between say 390F
and 400F on the display. That's a minimum
resolution of 250 MICROVOLTS.
This speaks to the unique requirement to
accurately measure and display tiny changes
in voltage with accuracy and stability.
As the article describes, accurate use of
a thermocouple requires a COMPARISON with
a temperature stable voltage most often
described as a 'cold junction' or 'reference
junction'. The voltage versus temperature
chart in 14-2 assumes a cold junction of
the SAME thermocouple materials held at
0C or 32F. I used to have a little Thermos
that was filled with distilled water and
ice frozen from that water to offer
a very accurate 0C reference bath.
Any instrument designed to accurately
DISPLAY real time temperatures based on
perception of thermocouple voltage must
include some form of cold-junction
reference in it's construction. It doesn't
need to be an ice-bath, only an accurate
voltage source that is microvolt stable
with respect to temperature. Not difficult
with modern electronics but not trivial
either.
Harly's observation is right on . . . if
your thermocouple shows a low resistance
continuity, then the thermocouple is not
OPEN. If it shows continuity to the mounting
enclosure, it may STILL be okay if the
companion instrument is designed to tolerate
certain noises that ride in on the thermocouple
leads that are remotely grounded to the system.
So there are two easily detected failure modes
for a thermocouple. (1) It may be completely OPEN
or (2) shorted to ground when it should not be.
Any attempt to measure the thermocouple with
a the most sensitive scale of a voltmeter
will be unrewarding. You might see some wiggle
in voltage based on changes in temperature
but offer no significance associated with the
magnitude of observed readings.
MOST manufactured thermocouples are K-type
and will be compatible with MOST multi-meters
having a thermocouple-style probe plug.
[img]cid:.0[/img]
I have a couple of meters fitted with such
sockets that purport to measure temperature . . .
and they're pretty good. But not as good as
a device specific to the task like a thermocouple
reading instrument by Fluke, Omega, and capable
competitors.
Further, just as we've see some great improvements
in accuracy and utility of digital multimeters,
it's reasonable to expect improvements in task-
specific meters too. I've ordered one of these
critters off eBay
[img]cid:.1[/img]
. . . $5 delivered to my door. I'll see how accurate
it is . . . and how well it compensates for local
ambient (cold junction issues). In ANY case, I'll
bet it is a useful trouble-shooting tool for seeing if
an installed thermocouple and associated wiring is
in-the-ball-park okay.
But if you're wanting to check the CALIBRATION of
your as-installed thermocouples, the only way is to
compare ship's readings with an independent measurement
using probe grade wire and an instrument of known
integrity.
Bob . . .
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