Could any DE-5000 user please confirm my way of measuring the inductance? - Page 1
Forum section: electronics / testgear

author: fishandchips
author_rank: Regular Contributor
timestamp: May 07, 2017, 05:07:41 pm
content: Hello, I bought a DE-5000 LCR meter. I connected the two alligator test leads (TL-21) to the terminals of a standalone DC motor. On the display, it showed L = 80 micro H, 1K Hz and Q = 0.579. Am I correct that the inductance in this case is 80e-6 H?

author: TimFox
author_rank: Super Contributor
timestamp: May 07, 2017, 10:12:53 pm
content: I would change the setting from Q to Rseries, and check the Lseries at 100, 1000, and 10kHz (not auto select).As somebody else pointed out, be very careful not to rotate the shaft, since the back emf could damage the DE-5000.

author: fishandchips
author_rank: Regular Contributor
timestamp: May 07, 2017, 11:08:58 pm
content: Quote from: TimFox on May 07, 2017, 10:12:53 pmThanks for the warning.How to do that? Do you mean by pressing the FREQ button? I got the following:Test1: On screen 100 Hz, Auto LCR, APO 0.4 degrees, 8.17 Ohm with theta symbol on top and Rs on the leftTest2: (pressed FREQ button twice): On screen 1kHz, Auto LCR, APO 3.9 degrees, 8.226 Ohm with theta symbol on top and Rs on the leftTest3: (pressed FREQ button once again): On screen 10kHz, Auto LCR, APO 0.483, 78 microH with Ls on the leftThese values change sometimes.

author: rstofer
author_rank: Super Contributor
timestamp: May 08, 2017, 12:34:19 am
content: Quote from: fishandchips on May 07, 2017, 11:08:58 pmAPO -> Auto Power Off modePage 36 shows which ranges will work at which frequencies. If you get a reading at 100 Hz, you are in the 20 mH range or above.Page 11 shows Ls as series inductance versus Lp as parallel inductance. Same for Rs as series resistance versus Rp as parallel resistance.Working out the 100Hz test, you have about 8 Ohms at 0.4 degrees. At such a small angle, the inductance is insignificant and the resistance of the coil is 8 Ohms. The device isn't giving an inductance value because the frequency is too low according to Page 36.Same story with the 1kHz test, the resistance is still about 8 Ohms and the inductance is too low to measure.At 10 kHz you are getting an inductance value of 78 uH of series inductance. I'm not sure what the 0.483 is about, what are the units?http://akizukidenshi.com/download/ds/deree/DE-5000_manu_en2p.pdfI don't see how the coil can be 8 Ohms for these tests and yet come up with 0.09 Ohms for the current test. If we assume it is a small motor, why is the resistance 100 times smaller than my robotics motor (yours=0.09, mine=7)? I'm inclined to think that the 8 Ohms is correct and that there is something wrong with the other resistance tests. Something's wrong! But you have voltage versus current that supports the 0.09 Ohm value. Hm...On the other thread, I got 7 Ohms and 5 mH. The resistance is dead bang right - 3 meters, all about the same reading. The inductance could be a little iffy. Tomorrow I will have a DE-5000 so I'll see what I get. Most important test will be the resistance reading - does it agree with my very accurate bench meters?It turns out that 1/L is a huge factor in the motor equations so we can't just ignore the value.

author: fishandchips
author_rank: Regular Contributor
timestamp: May 08, 2017, 12:52:32 am
content: There is a Q symbol in front of the 0.483. The value is displayed on the top right of the screen (like the 0.004 on p.22 of the manual). No unit is displayed for this value.

author: rstofer
author_rank: Super Contributor
timestamp: May 08, 2017, 01:21:36 am
content: Quote from: fishandchips on May 08, 2017, 12:52:32 amPage 7 has an equation relating Rs, Ls, f and Q. From the calculation, I get 61.5 uH and the meter gets 78 uH so things are in the same ballpark. No inductance to amount to anything.But we still have that huge discrepancy with Rs. More about that tomorrow sometime.

author: shteii01
author_rank: Frequent Contributor
timestamp: May 09, 2017, 12:40:40 am
content: Manual. Download it. Read it.

author: fishandchips
author_rank: Regular Contributor
timestamp: May 09, 2017, 11:54:19 pm
content: How come even for the same motor, the DE-5000 gave me different L, R and Q values in different measurements? Even in the same measurements, some of these values keeps increasing or decreasing. I did not turn the motor as warned by others.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 10, 2017, 12:16:06 am
content: When the resistance is very low, the point contact of the probes with the terminals can make a difference in the quality factor (Q) measurement. Also, the position of the probes can make a difference as they can add inductance themselves. Before the measurement try to zero the meter (I don't know how the function is called on the DER) and, after that, between each measure try to keep the probes at the same position. The inputs of the LCR tend to be susceptible to these factors.