Guys, My HP 53132A counter works fine as a frequency counter. When I try to use it to measure time intervals (say, between two PPS pulses), the measurements are quantized in steps of 100ns. For example, if the two PPS are nearly aligned, the measurements will be either 0.0980us or -0.0020us. If the PPS are drifting with respect to each other, there will be a long string of (say) 0.100 000 0980 sec, and then another long string of 0.100 000 1980 sec, with no intermediate values. (I can send a TimeLab .TIM file showing this behavior to anyone interested.) This quantization appears on measurements using both front-panel inputs (1 and 2) and on measurements using only input 1 and the "COMMON: ON" setting enabled.
According to the manual, the time-interval measurement resolution spec is 150ps. The quantization effect on my counter is about 3.5 orders of magnitude worse than that. That made me wonder whether there was a problem with the counter. The 100ns quantization is the reciprocal of the 10 MHz timebase frequency, which seems like a clue. One might suspect that the internal interpolators were not working correctly. However, the counter passes all its self-tests including the specific interpolator self-test, and it seems to interpolate correctly in frequency mode. I ran the internal time-interval calibration procedure "CAL: TI QUICK" with no errors, using a fast CMOS logic output for the required square-wave input. (Before my "QUICK" cal, the measurements were reported as 0.0965us and -0.0035us, so the cal procedure did actually change something, but it didn't fix the quantization problem.) I can't run the "CAL: TI FULL" procedure because it requires a specific HP calibration fixture. The procedure in the operators manual procedure for time-iinterval measurements doesn't seem to contain any tricks. Making TI measurements with and without an external timebase connected produces the same quantized results. I'm trying to figure out whether this quantization effect is expected behavior, operator error, or a problem with the counter. Any thoughts? Cheers! --Stu _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
