Digital Clamp
Posted on | February 27, 2010 | Comments Off
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New Uni-T UT203 Current Digital Clamp Meter DC/AC 400A |  |
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New UNI-T Digital Clamp Multimeter UT208 | |
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Digital Clamp
What is the best voltage limitation method before feeding an analog digital converter?
An analog amplifier circuit (gain = 25) is followed by level shifter (gain = 0.5, offset = 2.5V). The level shifter feeds an ADC with an input range of 0 to 5V. Between the level shifter and the ADC input there are 5V zener and clamping diodes with appropriate current limiting resistors in between. However the input voltage to the ADC still exceeds the range by the forward voltage of clamping diodes (i.e: -0.7 to 5.7V). Especially for negative voltages this causes the ADC to return erroneous values for other inputs using the same internal S&H circuit. What is the best way to achieve true voltage limiting without adding specialized IC's that may become obsolete in a few years?
One solution is to add accurate comparators to sense that the input voltage is below zero volts and above 5 volts and then send alarm data bits back to the processor that handles the data. But the comparators have to be adjusted to be more accurate than the AD.
Another solution is a better AD, or one that returns recognizable codes when the input is out of range. The processor than can see those codes and set appropriate flags.
Another is a precision clamp, reference has example. But the problem with this (and your solution) is that the processor will read an out of range voltage as an in-range voltage, which could be an error.
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How to do stitched panoramic digital photographic images.
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10 Top Tips For Macro Photography
10 Top Tips for Macro Photography
Go Steady
Camera shake can be a real problem at high magnifications due to longer exposures and shallow depth of field. Use a tripod or assume a sturdy position. Have the mirror lockup mode activated and preferably use a cable release.
Windy Conditions
Shooting macros of delicate subjects is impossible on a windy day so go equipped with a makeshift windbreak. A small clamp and stand may be enough to steady flowers and plants.
Props
Add impact to the shot and create an early morning feel with a water spray to imitate dew or rain.
Sharp as Possible
Maximise the depth of field by using an aperture of f/11 - f/22 and keeping your camera parallel to the subject. Use your depth of field preview button to see the result and if the preview is too dark, take a test shot and check the shot on your LCD.
Get Close
Ordinary lenses won’t let you get close to a subject. There is no substitute for a macro lens that can reproduce 1:1 or life-size reproduction. A focal length of 100 or 200mm will give a good distance to work from.
Manual Focus
Auto focus is a wonderful timesaving addition to your camera lens but can be tricky with close-ups as it battles back and forth to any subtle change or camera movement. Try switching to manual focus and choosing the focus point yourself. To make the most of the depth of field focus on the middle part of the subject.
Backgrounds
Try to avoid backgrounds of the same colour, otherwise your subject will blend into it. Clutter and patches of bright light will draw your eye away from the subject.
Fill in Flash
Add sparkle in dim conditions and reduce shadows and contrast on bright sunny days.
Get Light Subjects Right
With white butterflies for example standard camera metering can be fooled into underexposing so be prepared to add two stops of positive exposure compensation to eradicate this.
Diffused Light for Detail
Avoid burned out highlights and maximise fine detail by shooting on bright overcast days when the light is diffused and not harsh and direct. If you can’t avoid shooting in direct light then use a diffuser to soften the light.
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About the Author
Hi I'm Danny. 35 year old family man. Reside in the South of the of the UK. I don't have a lot of experience in article writing but I do have a lot of experience in life and will try to help people know anything that I know. My knowledge and experiences might be helpful to someone and that will make me happy!
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