[color=rgb(102,102,102);font-family:'Lucida Grande', Lucida, Verdana, sans-serif;font-size:13px;background-color:rgb(245,245,245);]Does anyone know a good op-amp implementation of a "Valley Detector", which I assume would be what one calls the opposite of a peak detector? I need to find the baseline of a signal so I can reject it. I want to do an op-amp circuit instead of with a DAQ so I can do it in real time.[/color]
[color=rgb(102,102,102);font-family:'Lucida Grande', Lucida, Verdana, sans-serif;font-size:13px;background-color:rgb(245,245,245);]I'm dealing with DC signals, if that makes a difference. The "valley" is a positive nonzero voltage.[/color]
Building a "valley detector"
#1
Posted 24 June 2013 - 09:24 PM
#2
Posted 24 June 2013 - 10:37 PM
#3
Posted 24 June 2013 - 10:42 PM
Couldn't you just invert the signal (turning valleys into peaks) and then apply a peak detector on that?
I could be wrong, but I think Inversion is not a valid technique here since all signals are nonzero and positive. This isn't an AC signal.
#4
Posted 24 June 2013 - 11:06 PM
#5
Posted 24 June 2013 - 11:25 PM
I meant for you to subtract the signal from a positive voltage.
It's a 30Hz square wave sitting on top of about 8 volts driven by photocurrent from thermal IR. I need to be able to dynamically adjust against that background.
#6
Posted 24 June 2013 - 11:36 PM
#7
Posted 25 June 2013 - 12:00 AM
I don't quite follow, I thought you were trying to detect local minimums but are you in fact trying to filter out the 8V DC component leaving just the square wave?
And amplify the difference. The big picture is to dynamically remove the background, as it's not a constant 8V, but varies from 0-10V.
#8
Posted 25 June 2013 - 08:25 AM
A stupid question perhaps, but if the background is also available on its own (without the square wave) a differential amplifier would do the job. I suspect not but provided the 8 - 10V signal varies significantly less (slower) than the square wave, you can use a high pass filter to isolate the square wave which could then be amplified. That is, you would design a filter to remove everything below the maximum frequency of the squarewave (e.g. place the knee at ~30Hz).
#9
Posted 25 June 2013 - 04:14 PM
A stupid question perhaps, but if the background is also available on its own (without the square wave) a differential amplifier would do the job. I suspect not but provided the 8 - 10V signal varies significantly less (slower) than the square wave, you can use a high pass filter to isolate the square wave which could then be amplified. That is, you would design a filter to remove everything below the maximum frequency of the squarewave (e.g. place the knee at ~30Hz).
Currently, the idea is to extract the background with LabView and feed it via analog output to a differential amplifier. It's not strictly available on its own, since the entire signal comes from a single sensor.
#10
Posted 26 June 2013 - 05:43 AM
#11
Posted 26 June 2013 - 07:41 PM
Ok, so basically you'll be using a software hp filter then, I suppose there are ready made functions for that in LabView but designing one in h/w is quite simple, basically you put a capacitor in series with a resistor to ground.
Might give this a try. Thanks!
Edit: gave it a try. It worked, but not as well as our current filtering idea which is the LabView-provided minimum for the differential amp.
#12
Posted 27 June 2013 - 07:55 AM
Ok, there are of course much more sophisticated hp-filter designs that you could apply.
Also tagged with one or more of these keywords: peak, valley, op amp, op-amp, circuit
General →
General Discussion →
Scale AnalogInput from Vref 1.8v - 30vStarted by slomobile, 11 Jul 2013 Signal Conditioning, scale and 5 more... |
|
1 user(s) are reading this topic
0 members, 1 guests, 0 anonymous users