Need info on a "Watt transducer" - Page 1
Forum section: electronics / projects

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 20, 2023, 07:59:48 pm
content: HeyI just picked up this thing on a whim, I though it may be useful for something.This device seems pretty simple, it measures power by sensing current on the wire running through the body and voltage on terminals 1 and 2. It also says it can measure anything from DC to 200kHz!!However I noticed that it says 230/380/460V on the voltage sense terminals, does that mean that it will not work properly for lower voltages, such as 120VAC or even lower AD or DC?I have not been able to find any information on this device, the company is gone and I can't find even a picture of another one, could the serial number of 00004 be factorPictures attached below.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 20, 2023, 08:50:07 pm
content: Perhaps the “Control 120V” is the power supply for the unit. If that is the case the unit should operate but you would only lose half of the dynamic range.Could you open the unit to see what is inside? That would also give you a clue whether the supply’s input requirements may be modified.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 20, 2023, 08:53:28 pm
content: I think the terminals labeled Control 120V (3 and 4) is the power supply? I really wish I could open it up but this thing is a solid block of resin! :'(

author: Siwastaja
author_rank: Super Contributor
timestamp: May 21, 2023, 12:53:15 pm
content: Confirm using a multimeter (hi-pot isolation tester would be really better) that the "control 120V" which I too assume to mean power supply is indeed isolated from the voltage measurement path. Then hook it up and try. As it says DC - 200kHz, it would be weird to have an arbitrary voltage limit either. Although one could assume from the voltage ranges that accuracy with lower voltages would be quite crippled - specifications are usually some % of full range, and less range you use the worse it is.Specifications are quite impressive, but being some hall type or similar (clearly not CT as the BW starts from DC) with full range of 100A, don't expect good DC accuracy on small currents; probably a few amperes of DC offset. Hopefully that "CAL" multiturn potentiometer means current DC offset calibration.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 21, 2023, 01:14:34 pm
content: I checked it, it is isolated, my multimeter just reads OLWhat output should I expect when I hook it up? Yesterday I set it up on 120V for the power and the sense, then I ran about 2 amps through it with a big lightbulb. With an oscilloscope the output was just a bunch of evenly spaced spikes that didn't seem to change with whatever I put through it.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 21, 2023, 02:02:04 pm
content: 2A is just 2% of full range. Try higher current. You can just loop the wire through the core multiple times to get the same effect without actually needing high current.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 21, 2023, 11:08:09 pm
content: I tried it again with some loops of wire, my clamp meter said 11A. Still there was no change on the output. I assume that the output is supposed to just be a DC signal, which it is not.It is quite likely that this thing is broken, the thing with the store that I get this stuff from is that items are there for a reason, so either somebody had this device sitting around and had no use for it, or it was removed from a system because it didn't work, and then wound up at the junk shop I frequent.Nonetheless this thing is interesting, I will keep my eye out for something similar. I go to that junk shop every weekend, it's a problem

author: Phoenix
author_rank: Frequent Contributor
timestamp: May 22, 2023, 02:44:12 am
content: Does pulse frequency change with power? Like the energy meters.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 22, 2023, 03:23:47 am
content: Perhaps? at the moment It wasn't giving me a good signal like it was earlier.I will test it more tomorrow, right now its 11:30 for me.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 22, 2023, 10:24:12 pm
content: Did a test, I don't think the frequency changes. The frequency is almost exactly 60Hz, so perhaps this is just ripple noise.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 22, 2023, 11:24:55 pm
content: simply put it must be based on a coil and circuitryhavent found anything on thisand the supply voltage is high .... must be like a clamp meter with added electronics giving an x ratio over x currentfor sure it is intriguingrockport give ME Maine

author: james_s
author_rank: Super Contributor
timestamp: May 23, 2023, 12:26:12 am
content: Open it up and see what's inside it. It's pretty obvious that there's a current transformer under that hole in the side. The rest of the circuitry is probably not complicated.

author: duak
author_rank: Super Contributor
timestamp: May 23, 2023, 03:26:12 am
content: I vaguely remember something called a pulse width, pulse height multiplier. It performs an analog multiplication by generating a pulse with the height a function of the X input and the width a function of the Y input. If the circuit operates at a constant frequency, say the line frequency, and the X input is driven by the line voltage and the Y input is driven by the load current, the area of the pulse is the power because it is the product of the voltage and the current. The pulse output has to be filtered, especially with a digital meter.Watt transducers appear to still be in production and are discussed generally in this document:https://www.ohiosemitronics.com/uploaded/resources/pdfs/Technical%20Notes/Transducer.pdfInput phasing appears to be important - try reversing either the voltage or current and try again.I couldn't find much on the technique itself but here's a patent that discusses a circuit that multiplies, divides and square roots:https://patentimages.storage.googleapis.com/00/ae/db/e5cf546b850a59/US3712977.pdfMore than needed but I hope it gives the general idea.Cheers,

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 23, 2023, 04:37:39 pm
content: Interesting, I will try reversing the current and see if anything new happens.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: May 23, 2023, 04:48:55 pm
content: I am not sure what to make of this, I attached two pictures of scope captures.I noticed two things, first is that reversing the phase of the current or the voltage did not change the initial output with no load. However under load the output goes from that ripple to just a DC value, but only after I reversed something, without reversing anything it continues to be a sine wave.I was not able to detect a noticeable change in the frequency or amplitude of the output with more load, except that under load the output is much cleaner?