Electronic – What determines the frequency range of a current transformer

current measurement

Per the title, what physical or construction parameters determine the frequency range of a current transformer? I happen to be looking at these two from mouser, but I'm sure the question is generic enough to apply to a large number of these things… What causes there to be a thousand-fold different in the minimum frequency?

Also, what happens if you attempt to measure a frequency well outside the rated range? For example, if you tried to measure a 50-60Hz residential power waveform with one of these KHz-range devices?

CT #1 : ICE CT08-1200 – listed as 40Hz – 200KHz

CT #2 : Murata 56200C – listed as 20KHz – 200KHz

Best Answer

The lower frequency limit is defined by how many volt-seconds the core can handle without saturating out. Generally, the smaller the core, the higher the minimum frequency, since a higher frequency means smaller on-time and lower volt-seconds for the transformer to deal with.

(Most CTs use ferrite cores, so if there isn't a specified \$ B_{max} \$ you can try 0.22T and figure out what volt-second product you can achieve with your specified burden resistor.)