inductive coil matching

[gianko25]

Dear All,

i have a M series 6289 and i want to acquire the signal from an inductive coil passed through a short pulsed magnetic field (200 us ramp rate, 600 us of flat top). The coil is connected to the differential input of my DAQ through a coax cable of 50 ohm impedance. the coil values are R=11.02 ohm and L=26.07 uH . How can i adapt the coil to the input to avoid voltage reflection and the delay?

Thanks in advance 

[EBL]

Hi, gianko25.

It depends on how long your coax cable is, but as long as it's under 20 feet or so, I'd try a shunt snubber right at your coil. The snubber would consist of a 47 nF capacitor in series with a 50 ohm resistor; this series combination would connect across the two terminals of your coil and would absorb any high-frequency reflections in the cable but leave your waveform largely undisturbed. Depending on the actual waveform, and the actual input capacitance of the 6289, etc., you may have to experiment with the capacitor value.

I'm not sure what you mean about avoiding the delay, but you cannot overcome the delay of the cable, unless you're prepared to build a time machine.

Hope this helps,

EBL

[gianko25]

Thanks i will try with shunt snubber. If i well understood i should put the capacitor in betwwen the two terminal and the resistor in series with one terminal ( or i should split the 50 ohm between the two terminals?). The values of C depends on the load?I mean,does it depend on the L value that i wrote above or is only function of the input capacitance of 6289? The 6289 capacitance is 100 pF for each channel so if i acquire in differential mode it should be the series between the two channel so it is 50 pF, is ti right?

About the delay i know, the important is that i can avoid at least delay up to 2.5 us (the sampling period)

Thanks

[EBL]

The 50 ohms is to match the cable, and the 47 nF is based on the R and L values of your coil. The input impedance of the 6289 doesn't make much difference.

The resistor and capacitor should be connected in series. Then that R-C series combination should be placed across the coil terminals, which should remain connected directly to the coax.

Hope this helps,

EBL