On 11/05/2015 10:50 AM, Jeff via vcf-midatlantic wrote:
So what does one do with a pulse generator, and how is it any different from a signal generator?
Pulse generators generate pulses. That's not a snotty reply; I will explain. On a typical test bench there are many different devices which produce and provide electrical stimulus of various sorts. Some are simple ones, like power supplies for example. We generally know what they do, and it's easy to understand why there are many different types with different capabilities, strengths, and weaknesses. As with many things in electronics, it starts out easy but becomes very complicated from there, and many things have somewhat poor names, for historical reasons. Changing those now would create chaos...look how long it took society to move from "cycles" to "Hertz", for example...now move that from everyday use to a group of educated people who pride themselves on terminological accuracy. (people who say "caps" notwithstanding) The term "signal generator" is one such instrument. It's a very vague name...after all, a bench power supply could correctly be called a signal generator, but people would look at you funny. No, the term "signal generator" generally means "a device that generates an as-close-to-perfectly-sinusoidal-as-possible RF signal with controllable frequency and amplitude, possibly with various forms of modulation". "RF" in this case is very generally considered to be anywhere from a few kHz well up into the terahertz range. Signal generators are optimized to perform this task...usually no other. A pulse generator is more precisely named. They generate mostly square waves, but not necessarily symmetrical ones. An electrical pulse has a great many parameters: Frequency, relative phase, peak-to-peak amplitude, positive and negative amplitudes, width, duty cycle, rise time, fall time, overshoot, undershoot, etc. A pulse generator is optimized to generate pulses in which many or all of those parameters are controllable. The term "pulse generator" carries with it no industry-known connotation of frequency range, but most common ones handle anywhere from a few uHz up to a few hundred MHz. A close relative is the function generator. The context of the term "function" in this case is mathematical. They generate waveforms of different shapes (defined by different mathematical functions); the most basic ones produce sine, square, and triangle waves. More advanced ones produce rising and falling ramp waveforms. All have configurable amplitudes and frequencies. These instruments typically go from the uHz range up to a few dozen MHz or so. So, as far as what one would do with a pulse generator. Today I am doing some testing on an industrial controller that I designed for work. One of the things it does is measure fluid flow using a sensor that generates pulses that correspond to flow, a certain number of pulses per unit of flow volume. It's not easy for me to set up calibrated fluid flow for hours at a time in my lab, so I use a pulse generator (HP 8161A) configured to make pulses that look just like the ones the real fluid flow sensors make. I can trivially change the pulse rate to work on the pulse rate linearization routines in my board's firmware...the real flow sensors' pulse outputs are not linear across its range of flow rates; the number of pulses per unit of volume changes as the rate of flow changes, and I've mathematically modeled that in my firmware so as to "undo" its effects and arrive at real numbers. Hope this helps.. -Dave -- Dave McGuire, AK4HZ New Kensington, PA