Current measuring pref a currentclamp

[flaxo]

Hi!

I need some help choosing the right sensor to measure current.
The idea is to be able to measure a single phase from a 3-phase motor with rated current of 75A ( bonusstar if it can handle up to 445A) and the signal from it should be received by a DAQ.
The input card can take care of 20mA (-20 to +20mA) or 10V (-10V to +10V) and has 50Ω impedance on the current mode and 107kΩ on the voltage mode.

The crux of the matter is that the installation should preferably not be invasive as the idea is that you can easily move around the measuring points. I started by looking around a little on current tongs but was limited by the low maximum current on the card. Also looked at solutions where the signal was a voltage such as fluke i200S but where the requirement for 1MΩ as input impedance put a spanner in the works.
Will there be major errors if I use the i200S?

Or is the best alternative a split core current transducer and run a current divider, worst case.

Excuse my bad English..

[Terry Bites]

http://www.pemuk.com/products/rct-industrial-sensor/rctrms-3-phase.aspx?
You need to be careful if you have a VFD most current transformers are rated for 50 or 60Hz. Rogowski based sensors have wide bandwidth.

[flaxo]

I missed to mention that they are all direkt drives (for now), so no VFD. I got my hands on a i400S is there any idea to order parts to be able to go from BNC to screwplint or will the impedance missmatch screw things over for me and in what way?

[Terry Bites]

If you make up your input impedance to 1M by adding a series resistor you can set your calibration error to a known figure. Of course the reading will be 5% ish of its true value. (10700000/(1000000+1070000)).  But 50% ish on the 10mv/A setting. Which you may be able to compensate for with a simple gain factor in your DAQ.
You can bypass the big resistor with a small cap to reduce noise. Again your DAQ probably has filters you can set. Keep the bandwidth as low as possible.

Some kind of calibration will be needed. This will be the hard part I expect.

[The Electrician]

Even though the spec for the i200s: https://www.fluke-direct.com/pdfs/cache/www.fluke-direct.com/i200s/datasheet/i200s-datasheet.pdf

mentions a load impedance of >1 MΩ // 100 pF, It says the output impedance for the 20A range is ≤ 20 Ω @ 1 kHz, and for the 200A range it's ≤ 10 Ω @ 1 kHz.  I would think your card input impedance of 107k should work just fine.