Tom Tom Van Baak wrote: >> I would also worry about long-term stability of any optical >> emitter and sensor pair. Any decline in light output over >> time might appear in the data as a phase shift which could >> affect amplitude or period stability. Then there's any tempco >> or voltco issues to consider with optoelectronic elements. >>
The usual solution to this is to use analog circuitry to calculate (I1-I2)/(I1+I2) rather than just (I1-I2) although the location of the point of equality (of I1 and I2) is independent of I1 and I2 provided that the responses of the 2 sensors track. I1 is the photocurrent from sensor 1, I2 is the photocurrent from sensor 2. > By the way, a really nice technical paper on a precision > pendulum clock is this 1996 paper by De Marchi: > > A Measurement of the Period Stability of a Free Pendulum > http://www.leapsecond.com/history/1996-DeMarchi-Pendulum-Stability.pdf > > Clever solution. His optical gap is something like 5 microns. > Suitable spheres are available from edmund optics. http://www.edmundoptics.com > /tvb > Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
