AC and DC Current Sensing

I'm interested in sensing AC and DC currents, 0-8A nominally, but up to 160 A for 10msec current surges from both AC and DC sources... I'm after the be st resolution I can get... I don't know if it's possible to do this for bot h AC and DC off the same current sense circuit... I was thinking a shunt th rough a current sense amplifier then to an RMS to DC converter IC... but I' m not sure if this is the best approach... any suggestions?

much thanks!

Reply to
panfilero
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The Danfysik DCCTs are fantastic.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

If it's at a convenient common mode (like connected to GND), a shunt can work. You need a small enough resistance of course.

Hall effect sensors are also useful in that range.

Tim

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Seven Transistor Labs 
Electrical Engineering Consultation 
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Reply to
Tim Williams

On a sunny day (Mon, 14 Apr 2014 20:57:11 -0700 (PDT)) it happened panfilero wrote in :

I have some nice Hall sensor based DC sensors.... No shunt losses.

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There are lower current models too.

Reply to
Jan Panteltje

60A for 10msec current surges from both AC and DC sources... I'm after the best resolution I can get... I don't know if it's possible to do this for b oth AC and DC off the same current sense circuit... I was thinking a shunt through a current sense amplifier then to an RMS to DC converter IC... but I'm not sure if this is the best approach... any suggestions?

Hello !

In such situation i may say "Please avoid any design based on a resitor shu nt". Although most of engineers are thinking about shunts, thinking it may produce a clean and low cost PCBA, in fact it will not ! believe me, chosin g a shunt for such current will drive you crazy ... you are warned.

The only best choice for

- DC/AC large range of currents, - sustain surge current, - galvanic insulation, - ...etc

is a Hall effect closed loop CT. --> try googling with.

Habib.

Reply to
habib.bouaziz

Once for monitoring giant industrial control system, I designed a universal, low-cost, isolated sensor. This isolated, extremely low cost/wide range multi-'voltage' sensor was used as the input(s) into multiple sets of 8, or 16 analog input GNDed MUXes for computer system measuring multi-voltage ranges [important characteristic to have universal measurement range, sensors interchangeable, and exact types unknown to the installer] for monitoring DC/AC switches and DC/AC motors in 'electrically robust' industrial applications. Since basic sensor actually used a resistor to be high impedance and the sensor actually measured current through that resistor, you could adapt the basic design to your needs.

The sensor met the following: DC/AC: 'voltmeter' [DC, or AC mains switches, motors, etc] INPUT: input required less than 1/2 watt max OUTPUT: analog waveform RANGE: 'accurately' measure unknown sources of +/-5Vdc to 480Vac [200ppm of FS, remember, sensing current] ISOLATION: 3kVac [standard high quality transformer, UL/NRTL approved. Note, at the input's isolated voltage there were two terminals, two resistors, a capacitor, and the input to the 3/8 inch transformer so the PCB area for creepage distance, etc was SMALL!] POWER SUPPLY: used available +-12Vdc, less than 200 mW per sensor COST: $.87 per sensor

These racks of sensors provided inexpensive monitoring in sets of 8 to 16 isolated pairs that then could be put into the computer's GNDed 8, or 16, to 1 analog MUX for the computer to do its ADC on. Sets of sensors, because some Systems required over 100 monitoring points, some Systems much less. The application was for a pretty complex industrial computer control of a 'monster' of an industrial system. controlling a myriad of motors while monitoring all kinds of supply/running voltages and position ON/OFF type switches. At each installation, the computer control system was identical, yet each installation/application was absolutely different at each of those locations. To lower costs, the overall installation had to be 'universal' without regard to what was being monitored, whether it was a 5Vdc switch, or a 480Vac motor supply. Even the computer system was set up to 'learn' what was connected to it. Cabling was a nightmarish jumble. The motors were, well, BIG! Moving several tons around. Electrical environment? When everything was running the EMC was enough to shut off your hand drill, not really, but very, very robust interference. Industrial grade EMC AC mains requirements, with motor switching noise in excess of 1000 Volt spikes and surges type noise.

If you have a 'volume' requirement, or need 'universal' inexpensive isolated input sensors; contact me. The design can be adapted.

Reply to
RobertMacy

Are you only measuring the 0-8A, and just tolerating the 160A surge, or do you need to measure the 160A as well? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Re-inforce what you say, with

  1. don't want to mess with those kinds of power connections - leave them intact.
  2. better to have isolation to those lines, you have no idea what they're doing.
  3. Don't insert anything.

PS: I don't like Hall-effect sensors because they are current hogs and drift.

for 'one offs' I'd look at GMR sensors, readily available, like Hall Effect, but only require around 1-2mA bias current.

NVE Corporation (800) GMR-7141 (800) 467-7141

11409 Valley View Road Eden Prairie, MN 55344
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Reply to
RobertMacy

Oh Hall effect sensors are not so bad, they have decent di(t)/dt, quite linear, easy sensor conditionning ... well thermal drift is a problem and also not so linear on small magnetic fields, but it's AFAIK the only(?) relatively low cost solution for large range of AC/DC currents. Fluxgate technology is also an option ... no experiences on that topic.

GMR sensors seem promising, thaks for the nve.com link. I will remember next time.

PS : No further trivial explanations for experienced engineers about shunt sensors on large range currents (CMRR, lack of insulation, totally un-rugged against IEC61000-4-5, -4-3, ...etc ...) ...a nightmare.

BR, Habib.

Reply to
Habib Bouaziz-Viallet

Yup, that's the right question ;-)

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Thanks, 
Fred.
Reply to
Fred Bartoli

I have a couple of current clamps for scopes or DMM coming that can do like 20mA up to 65 or 650 Amps scaled to mV.

These only have 20khz response time but close enough for what I want them for and the price is acceptable since the upper units can't seem to do much better, so why pay for them?

Jamie

Reply to
Maynard A. Philbrook Jr.

160A for 10msec current surges from both AC and DC sources... I'm after the best resolution I can get... I don't know if it's possible to do this for both AC and DC off the same current sense circuit... I was thinking a shunt through a current sense amplifier then to an RMS to DC converter IC... but I'm not sure if this is the best approach... any suggestions?

Measure the 160A surge as well... I'm thinking a shunt (2mOhm or so) with a n isolated sigma delta converter right now....

like this guy:

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Reply to
panfilero

What voltages are involved? 220v? If you working with higher voltage you should go for some type of isolation, more than that converter provides. As others pointed out, Halls would work. I have a 300A ACDC FW Bell Hall effect current sense module around here somewhere.

Cheers

Reply to
Martin Riddle

I have some 50A FS something or other around here, combo of current transformer and Hall device, that I used for the Bosch motor control project... I'll post info upon finding. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

" No shunt losses". OK, since we all know that TANSTAAFL, would anyone care to estimate what the additional impedance of running a wire past a Hall effect sensor is? It takes real force to push those electrons and holes around, you know. Just the thought of calculating the answer makes my brain hurt.

Reply to
Ralph Barone

On a sunny day (Tue, 15 Apr 2014 18:14:08 -0400) it happened "Maynard A. Philbrook Jr." wrote in :

Yea, that would work too, size? I payed 4 Euro for these...

Reply to
Jan Panteltje

On a sunny day (Wed, 16 Apr 2014 02:19:59 GMT) it happened Ralph Barone wrote in :

You could avoid that pain by spending 6 dolars and measuring it? Or is measuring no longer of this age, and is slimulation required?

Reply to
Jan Panteltje

On a sunny day (Wed, 16 Apr 2014 02:19:59 GMT) it happened Ralph Barone wrote in :

You could avoid that pain by spending 6 dolars and measuring it? Or is measuring no longer of this age, and is slimulation required?

PS There is an other way:

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That is an old playback head from a walkman against a mains lead. Very little losses in the straight wire, very good frequency response (to kHz). You can set the sensitivity by moving the head further away. High output voltage (directly into opamp here). Good linearity (audio like). :-) But, again, it needs calibration, send 1A current measure output, you repeat for other currents, get curve,,, No slimulation will do that for you. Cannot beat the price I think. Good isolation too.

Reply to
Jan Panteltje

I have three of the LEM-50A units. Nice! ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

It's a good solution, for AC; the possibility of high DC currents, though, means that one might possibly have to attend to demagnetizing the playback head in order to keep it calibrated. Tape head demagnetizers are intended, after all, to change the head's properties using nearby currents!

Reply to
whit3rd

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