adamp
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Posts: 14
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Post by adamp on Dec 16, 2022 13:51:01 GMT -5
I am trying to measure the field strength of a permanent magnet assembly using the F71 and was curious about how probe temperature will influence my results. At the moment it seems like my measurements are dependent on the temperature of my probe and not the temperature of my magnet, which is not the experience we have with the 475 Gaussmeter.
I know from experimentation and manufacturers specification that our magnets field strength can be related to it’s temperature by the equation below: B(T_m) = B_0*(1+(T_m0 -T_m)*c_m)
Where T_m is the measured magnet temperature, B_0 is the field strength measured at temperature T_m0, and c_m is the magnet temperature coefficient (~0.1%/°C).
From what I’ve gathered the probe has a similar relationship for it’s temperature compensation B(T_p) = B_p(T_p)*(1+(T_p0 -T_p)*c_p)
Where T_p is the probe temperature, B_p(T_p) is the temperature sensitive field measurement, T_p0 is the temperature that the probe was calibrated at, and c_p is the probe temperature coefficient.
From this is it fair to assume the following operating assumptions?
1. When the magnet temperature remains constant (and its field remains constant), but the probe temperature fluctuates, you would expect the probes field measurement to remain constant, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect see a horizontal line.
2. When the magnet temperature fluctuates (and its field fluctuates as well), but the probe temperature remains constant, you would expect the field measurement to change, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect a vertical line
3. When the magnet temperature fluctuates (and its field fluctuates as well), and the probe temperature changes independently of the magnet temperature, you would expect the field measurement to change, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect to see the data points distributed over the area of the plot with no clear pattern
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adamp
New Member
Posts: 14
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Post by adamp on Dec 19, 2022 12:45:26 GMT -5
I have been running single point acquisitions over the course of several days to establish the performance of the F71 for our applications and have been observing deviations in the reported field strength of up to 300 µT despite the fact that we are controlling our magnet temperature to less than 0.003 °C over that period. For that change in magnet temperature I would expect field deviations up to 10 µT. When I compare the reported field strength to the temperature of the probe I see a strong negative correlation: **probe temperature is in °C is this temperature sensitivity what I should come to expect form this instrument or are there any setting I can change to improve my measurements. For the record, we have several 475 Gaussmeters and do not observe this temperature dependency. |
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Post by Lake Shore Ryan on Dec 19, 2022 14:08:01 GMT -5
Hi, thanks for giving such detailed feedback. Could you please let me know the serial number of the probe so we can check the calibration file for the probe. Maybe that will give us some clues.
As for your original post, all three of your operating assumptions at the end are correct. However, our temperature compensation algorithm uses a gain table (many temperature/gain pairs) with linear interpolation between the points in the table used to determine the gain for any given temperature value. This allows us to deal with the non-linear nature of a Hall sensor's temperature dependence.
This table is not unique for every sensor though, it is set for each sensor type based on population testing completed prior to the product's release. it may be that this probe's actual temperature coefficient is further away from the population average than normal, resulting in the plot you've shown. Based on what we see from the calibration file, we can make suggestions on how this might be corrected.
Is the teslameter also being exposed to these temperature fluctuations?
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adamp
New Member
Posts: 14
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Post by adamp on Dec 19, 2022 15:20:25 GMT -5
Thanks for getting back to me Ryan!
I sent you a message with the probe serial number, I am interested to see what you guys find in the calibration file. Is there any chance I could get access to the calibration file for this probe as well as the compensation table, if it's not in that file?
The teslameter would have been exposed to peak to peak temperature fluctuations of about 1.5°C with a frequency of about half an hour. Do you have a sense for the temperature sensitivity of the teslameter?
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Post by Lake Shore Ryan on Dec 20, 2022 13:04:56 GMT -5
The teslameters accuracy specs are all defined within a ±5°C range, so small fluctuations like you saw shouldn't be a problem. I looked up your probe, and transverse probes like this (FP-2X-250-TSxxxxxxx) all use the same temperature compensation table: | Temperature (°C) | Gain factor | 0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
| 1.0014
1.001
1.0007
1.0003
1
0.9997
0.9982
0.9962
0.9951
0.9937
0.9925
0.9916
0.9907
0.99
0.9893
0.989
0.9886
0.9886
0.9886
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To check whether this is being applied properly, could you please try the test again with probe temperature compensation disabled? You should still record probe temperature and plot it against field strength, just ask the teslameter not to apply any temperature compensation. The results of this test will likely tell us whether there is an issue with the temperature compensation curve, or maybe some issue with the how the calibration was written or stored. Thanks. |
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adamp
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Posts: 14
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Post by adamp on Dec 20, 2022 14:19:37 GMT -5
I actually have run that test already, over the test the magnet temperature would have again been controlling temperature with a max deviation of 0.003 °C and the teslameter would have temperature fluctuations of about 1.5°C in amplitude with a frequency of about half an hour. We are still experiencing a large deviation in field strength over this period, roughly 250 µT, but you can see that there is no real connection between probe temperature and reported field strength now.
Here is another plot which shows the field strength and temperature over the test period. You can see there's a pretty steady increase in reported field strength over the period, but I really struggle to understand what could be causing that. The magnet temperature could be contributing a little to that, but by my estimate we would need to see an increase in temperature of 0.1°C to account for that much field change, which is about 30 times more change than our temperature sensors report.
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Post by Lake Shore Ryan on Jan 6, 2023 17:46:58 GMT -5
Thanks for this extra information. Sorry for the delayed response, was on vacation. I'll talk to some people here about what could be causing this and get back to you. Thanks for your patience.
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Post by Lake Shore Ryan on Jan 9, 2023 14:30:11 GMT -5
adamp, you wouldn't happen to have another probe that you can swap with this one would you? This problem may require an RMA for that probe so we can properly compare it with our calibrated systems and see if we can figure this out.
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adamp
New Member
Posts: 14
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Post by adamp on Jan 12, 2023 15:12:14 GMT -5
Yes, we have another probe I can swap this with. That test will have to wait until next week, as I have switched back over to the 455 to get some comparison data. I'll let you know how it goes with the other probe, I expect it wont be much different though.
I would be very happy to open the discussion for RMA, we have several of these Teslameters and probes that have been sitting on the shelf because they just don't meet our performance requirements.
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Post by Lake Shore Ryan on Jan 13, 2023 12:14:37 GMT -5
Happy to wait and hear back about your experience with another probe. I've also given the support team a heads up about your case, so they'll be ready if you reach out to them. They'll be able to accept your products back for testing on our calibration stations to confirm whether they're performing within specifications.
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adamp
New Member
Posts: 14
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Post by adamp on Jan 18, 2023 13:25:23 GMT -5
I reran the tests with the F71 equipped with a different probe and a 455 Gaussmeter for comparison. Over the course of about 20 hours the span of field measurements when using the F71 with a different probe was 500 µT, this was similar performance as what we had seen with the original probe. When this same test was run using the 455 Gaussmeter we see a span in field measurement of 29 µT. The temperature conditions of the magnet, probe, and Gauss/Teslameter during these tests were all pretty much the same, and I have summarized that information in the table below.
| 455 Gaussmeter with 400 series probe
| F71 Teslaeter with FP series probe #1
| F71 Teslaeter with FP series probe #2
| Length of data gathering [Hrs]
| 23
| 20
| 23
| Magnet temperature Span [ °C ]
| 0.00075
| 0.00122
| 0.00053
| Probe temperature span [ °C ]
| 0.198
| 0.52533
| 0.38988
| Field span [ µT ]
| 29
| 406
| 504
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As it stands, the performance and ease of use for the 455 is much better than the F71 for our application and I am struggling to see what can be done to improve the F71's performance. I'll send an email off to support to see what we can do. |
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Post by munirashraf9821 on Aug 18, 2023 6:15:15 GMT -5
I am trying to measure the field strength of a permanent magnet assembly using the F71 and was curious about how probe temperature will influence my results. At the moment it seems like my measurements are dependent on the temperature of my probe and not the temperature of my magnet, which is not the experience we have with the 475 Gaussmeter.
I know from experimentation and manufacturers specification that our magnets field strength can be related to it’s temperature by the equation below: B(T_m) = B_0*(1+(T_m0 -T_m)*c_m)
Where T_m is the measured magnet temperature, B_0 is the field strength measured at temperature T_m0, and c_m is the magnet temperature coefficient (~0.1%/°C).
From what I’ve gathered the probe has a similar relationship for it’s temperature compensation B(T_p) = B_p(T_p)*(1+(T_p0 -T_p)*c_p)
Where T_p is the probe temperature, B_p(T_p) is the temperature sensitive field measurement, T_p0 is the temperature that the probe was calibrated at, and c_p is the probe temperature coefficient.
From this is it fair to assume the following operating assumptions?
1. When the magnet temperature remains constant (and its field remains constant), but the probe temperature fluctuates, you would expect the probes field measurement to remain constant, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect see a horizontal line.
2. When the magnet temperature fluctuates (and its field fluctuates as well), but the probe temperature remains constant, you would expect the field measurement to change, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect a vertical line
3. When the magnet temperature fluctuates (and its field fluctuates as well), and the probe temperature changes independently of the magnet temperature, you would expect the field measurement to change, and if you plotted the relationship between measured field strength vs measured probe temperature you would expect to see the data points distributed over the area of the plot with no clear pattern
Hey, Munasir here! Your analysis on the impact of magnet and probe temperatures on the field strength measurement is spot on. Indeed, the temperature dependency of both the magnet and the probe can lead to varied results. To summarize: If only the probe temperature varies, your measurements should ideally remain consistent (assuming the probe's temperature compensation is functioning correctly). If only the magnet's temperature fluctuates, the field strength measurement will change accordingly due to the inherent temperature coefficient of the magnet. When both temperatures fluctuate independently, the combination of both effects will produce a more complex pattern of results, making interpretation a bit more challenging. It sounds like you've got a good grasp on the matter. Always crucial to consider all variables in such precise measurements! Keep experimenting and best of luck with your work!🧲🌡️ Warm regards, Munasir. |
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