dhenry:
Let RL=100, then appr. 100mV on RL translate to 1A... 200mV to 2A...
That "sensitivity" figure is specified at the rated current (of 25amp). So running 25amp Ip, you should expect about 2.5v (=100mv * 25amp) on the secondary. All rms of course. The datasheet doesn't say if that relationship holds if Ip is other than 25amp.
But check this data sheet http://www.soselectronic.com/a_info/resource/a/pdf/AC1050.pdf.
It gives you all the information we need. We can see it is approximate linear. So it should be the same value used to calculate the current, for a given burden...