Hello everyone,
I have a big request for help. Yesterday I probing simple circuit based on Arduino and TIP122 for 12V solenoids valves. I sending a short 20ms pulse to open the valve and trigger at the scope. Everything was fine until I set the scope scale to 500mV/div. Readings has unexpectedly changed and I have no idea why. I figured that the "transition" occurs between 750-760mV/div. Higher scale is ok (800mV, 1V, 2V...), but the "750" and below causes bad readings.
I know it sounds strange but please take a look at pictures and tell me what you think. Why a simple change of scale effect on the results? Is it something I'm doing badly?
Setup:
DS1074Z @ default settings, sw 00.04.01.SP2, hw 0.1.1
http://www.ecs.umass.edu/ece/m5/images/TIP122_transistor_schematic_S.jpgMeasured between GND and tip122 collector, pulse duration is 20ms
Screen captures:
pic_01 (5V/div)
pic_02 (1V/div)
pic_03 (760mV/div)
pic_04 (750mV/div)
pic_05 (500mV/div)
pic_06 (300mV/div)
Problems do not occur in other cases (at least, I haven't yet noticed ...). It seems that this particular example is somehow strange ...
For example, if I measure the base of a TIP122 everything is ok. The duration and all the rest are correct.
I'll be grateful for your help. Thanks in advance.
Best regards,
Krzysztof
Ask yourself what the voltage range of the signal you're trying to look at is. Then work out the full scale capability of each range you chose.
In fact, that's right. If I decrease the the voltage on the valve, "the problem" disappears. I appreciate your help. This is my first oscilloscope and I still learning
