meters for VFD drive measurements - Page 1
Forum section: electronics / projects

author: rakesh
author_rank: Unknown
timestamp: October 12, 2012, 04:46:50 am
content: hello everyoneAm using a kelly induction motor controller KIM7210. It generates a three phase AC from a 72Volts DC power supply.I tried to measure the parameters like voltage ,current and frequency using my protek multimeter. But when i do the calculationsbased on the input and output values there is a huge efficiency contradiction. So am planning to buy a new digital multimeter which would display the accurate value of the voltages ,current and frequency of the three phase waveform. The voltage i want to measure is a 40Volts 3 phase AC and Maximum current of about 50Amperes.So please suggest me a good meter which will have the low pas filter capability which would be immune to supply noise and woulddisplay the accurate values of the above said parameters. And also tell me whats your view on using fluke87V and Fluke 289 for vfd measurements.

author: Bloch
author_rank: Unknown
timestamp: October 12, 2012, 01:21:32 pm
content: Quote from: rakesh on October 12, 2012, 04:46:50 amWith a AC motor it is not enough to measure Volt and current to calculate Watt !When you have a AC motors then you need to learn about cos. And example of a nameplate is here (http://www.seai.ie/uploadedfiles/ACA/Motors%20template.jpgMore about theoryhttp://en.wikipedia.org/wiki/Power_factorSo you cant use a "simple" multimeter, but a true WATT meter.

author: rakesh
author_rank: Unknown
timestamp: October 12, 2012, 02:25:58 pm
content: thanks for your reply bloch. I do know how to perform all the input and output measurements for Ac motors. And by the way I have a power factor meter which measures the accurate value. All I need is a nice meter which would measure the voltage and current with a current clamp(the hall effect type). I thought of using the fluke87V for measurements but i read on the internet due to high switching frequency of the controller the multimeter won't display the accurate value.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 12, 2012, 02:43:50 pm
content: unless it is some sort of special vsd it probably puts out 0-100 hz which all multimeters will be able to measure.Of course there will be a lot a harmonics in there too but your calcs if done right, with an rms meter should be in the ball bark.Looking at the waveform on the cro might help.You could build your own low pass filter if you needed, with a resistor and a cap.

author: robrenz
author_rank: Super Contributor
timestamp: October 12, 2012, 03:16:30 pm
content: http://www.fluke.com/fluke/usen/community/fluke-news-plus/articlecategories/motorsdrives/measuringasds.htm

author: qno
author_rank: Frequent Contributor
timestamp: October 12, 2012, 03:42:46 pm
content: You can place a filter in front of you meter to integrate the high frequency.If you have a scope you can measure (filtered) voltage on channel 1 and current in channel 2 and multiply the 2. Then you have a graph with real power.Cos phi is changed by the load of the motor.

author: rakesh
author_rank: Unknown
timestamp: October 12, 2012, 04:49:05 pm
content: I got a tektronix oscilloscope with me which is tds1012B. since the ground lead is referenced to earth there is a immediate flow o current from the motor to the ground through the oscilloscope probes. After a further research i made the differential voltage measurement by removing the ground leads on both channels.But the waveform appears to be very much distorted since i couldn't interpret the accurate value using an oscilloscope i thought of buying a meter which would show the accurate value of current and voltage.And that is the reason i asked if someone could suggest me a nice meter.And also if am going to use the fluke87v for my vfd measurements with low pass filter enabled do i have to include any additional low pass filter circuit? and by the way the switching frequency of the controller is 16.6KHz

author: dmather
author_rank: Newbie
timestamp: October 14, 2012, 05:47:33 am
content: You could try an Agilent U1272A, they are supposed to be able to measure from VFDs.

author: glicos
author_rank: Regular Contributor
timestamp: October 14, 2012, 03:14:54 pm
content: Or an analog meter VOM.......