IET
 Topic Title: Analogue or digital Topic Summary: comparing an analogue integrator with a digital solution Created On: 30 April 2010 04:07 PM Status: Read Only Linear : Threading : Single : Branch
Search Topic
Topic Tools
 View similar topics Print this topic.
 30 April 2010 04:07 PM TCSC Posts: 175 Joined: 25 April 2007 Apologies if this is a discussed question. I have been away in the wilderness for many years. If you use an op-amp integrator on the signal from a tacho generator (velocity), you can produce a voltage propotional to how many revolutions the tacho generator has turned (distance). It is quite instructive and fun to do. However you have to deal with input bias and leakage currents etc. introducting erronous outputs. Instead it would appear to be much simpler to use a pulse transducer giving a pulse every few degrees of rotation, and simply clock a counter. The output of the counter is then converted from D to A giving a similar analogue display of distance. There would be no problems of errors or drift etc. It seems to me that for any sort of simple integration of a signal, a digital circuit would be more appropriate than the analogue. So my question is, - Are there any situations where an analogue integrator would be used instead of a digital one? Assuming that resolution or bandwidth isn't a limiting factor eg say you only wanted audio bandwidth and an analogue meter display. Cheers 30 April 2010 07:32 PM jencam Posts: 608 Joined: 06 May 2007 Originally posted by: TCSCAre there any situations where an analogue integrator would be used instead of a digital one? Here is an answer from my son. An analogue integrator is used in situations where a true mathematical integration of a signal is required. The signal being integrated is usually a continuously varying voltage or a train of pulses where the voltage and the duration of the pulses is likely to vary. In the case of the tacho generator, the number of pulses in a given timeframe is of greater importance than the voltage and duration of the pulses, so a pulse counter can be used instead of an integrator. Pulse counters replaced integrators in the vertical synchronisation circuits of some televisions during the early 1980s as they eliminated problems caused by component drift. It is possible to create a digital integrator using an A/D converter then performing the integration mathematically. The performance of these are subject to quantisation error and Nyquist. 05 May 2010 09:51 AM amillar Posts: 1918 Joined: 28 May 2002 Simplistically: If you want an accurate integration (step size and sampling apart) do it digitally. If you want a simple integrator do it in analogue. As you say, problems of bias and leakage currents, and also component drifts and non-linearities, make analogue integrators a bit of a nightmare. But practically an integrator will always form part of a larger system, so you tend to choose the technology to match the rest of the system: it is hard to image a digital control system that would exit into analogue just to implement an integrator (although it may make sense the other way around). The last time I used an analogue integrator* was nearly 20 years ago, to correct the DC offset in an audio system (to avoid the use of coupling capacitors), however this was inside a feedback loop so the exact parameters and stability were not critical. *Of course a low-pass filter is actually an integrator, but I think we know what we mean by treating them seperately... ------------------------- Andy Millar CEng MIET CMgr MCMIhttp://www.linkedin.com/in/millarandy"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert 05 May 2010 09:24 PM jencam Posts: 608 Joined: 06 May 2007 Originally posted by: amillar The last time I used an analogue integrator* was nearly 20 years ago, to correct the DC offset in an audio system (to avoid the use of coupling capacitors), however this was inside a feedback loop so the exact parameters and stability were not critical. Do analogue sample and hold circuits belong in the history books? 07 May 2010 12:33 PM amillar Posts: 1918 Joined: 28 May 2002 As far as I know they are still a key part of many (most?) A-D convertors ------------------------- Andy Millar CEng MIET CMgr MCMIhttp://www.linkedin.com/in/millarandy"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert 07 May 2010 04:35 PM saridgway Posts: 148 Joined: 07 May 2002 Originally posted by: TCSC Instead it would appear to be much simpler to use a pulse transducer giving a pulse every few degrees of rotation, and simply clock a counter. Provided the clock is free from noise (not always easy to achieve, as I was reminded when using a similar approach in a 7kW searchlight pan and tilt system a few years ago). ------------------------- Steve Ridgway MIET 10 May 2010 10:12 AM TCSC Posts: 175 Joined: 25 April 2007 Thanks guys. Interesting and useful answers.
 IET » Electronic engineering » Analogue or digital Topic Tools
Statistics