something odd with my Owon O-scope and hopefully someone can suggest a answer.
the scope is a PDS5022S. it has a self calibartion feature which i use from time-to-time. the scope doesnt read voltage correctly when i am reading the analog output of my circuit.
the circuit is a 555 that oscillates slowly around 1Hz 50%pwm. the output shown on schematic.
C1 is 22uF electrolytic
D1 is 1n4148
R1 << R2 << R3
so basically the voltage dividers give me the output voltages i want when 555 swings high and low.
weird thing is, my scope is reading the voltage oddly. when the 555 swings low the scope reads a voltage less than zero, and when it swings high it reads a voltage that is less than what my Fluke meter reads.
as example, if i set the output voltage (using Fluke) to +0.7v on the high side amd +0.1v on the low side, the scope reads -0.045v and +0.5v.
two things are odd. 1) the voltage swing isnt even correct on the scope. it should swing 0.6v, but the scope reads a delta of 0.545, so i thought maybe the calibration might be off, and 2) why the scope reads a less than zero voltage when 555 swings low.
so i re-ran the self calibration and then got a precision voltage reference IC which has several dc output voltages. weird, both my Fluke and scope read the exact same voltage on the IC. i also have on my desk a crude power supply, and both the scope and Fluke read the same voltages (dc and ac on the full wave rectifier).
...and yes, i did make sure the scope probe settings are all correct.
very weird. i am trying to figure out why the scope reads funny on this circuit. any suggestions? ...and yes, there are other parts connected to the 555, i didnt draw them for simplicity.
the scope is a PDS5022S. it has a self calibartion feature which i use from time-to-time. the scope doesnt read voltage correctly when i am reading the analog output of my circuit.
the circuit is a 555 that oscillates slowly around 1Hz 50%pwm. the output shown on schematic.
C1 is 22uF electrolytic
D1 is 1n4148
R1 << R2 << R3
so basically the voltage dividers give me the output voltages i want when 555 swings high and low.
weird thing is, my scope is reading the voltage oddly. when the 555 swings low the scope reads a voltage less than zero, and when it swings high it reads a voltage that is less than what my Fluke meter reads.
as example, if i set the output voltage (using Fluke) to +0.7v on the high side amd +0.1v on the low side, the scope reads -0.045v and +0.5v.
two things are odd. 1) the voltage swing isnt even correct on the scope. it should swing 0.6v, but the scope reads a delta of 0.545, so i thought maybe the calibration might be off, and 2) why the scope reads a less than zero voltage when 555 swings low.
so i re-ran the self calibration and then got a precision voltage reference IC which has several dc output voltages. weird, both my Fluke and scope read the exact same voltage on the IC. i also have on my desk a crude power supply, and both the scope and Fluke read the same voltages (dc and ac on the full wave rectifier).
...and yes, i did make sure the scope probe settings are all correct.
very weird. i am trying to figure out why the scope reads funny on this circuit. any suggestions? ...and yes, there are other parts connected to the 555, i didnt draw them for simplicity.
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