Adam wrote... >What about putting an integrator after the piezo? That's in fact what's usually done with piezoelectric accelerometers, and the integrator is referred to as a charge amplifier. However, there's no such thing as an integrator with zero leakage, either, so a piezo is still only good for measuring momentary forces. (The reason charge amplifiers are used with piezo accelerometers is to allow long cabling between the accelerometer and its instrumentation; if the accelerometer were used in "voltage mode" instead of with the charge amplifier, the cable capacitance would shunt the output and reduce the output voltage, requiring recalibration with every setup.) Dave D. >Dave Dilatush wrote: > >>David Harris wrote... >> >>>I'll wait ;-) >>>Can't we just use a piezocrystal -- maybe a buzzer -- stretch and measure. >>> >> >>The problem with those critters is that they only produce a momentary >>output. >> >>If you had a perfect measuring instrument, with infinite input impedance >>and absolutely zero leakage current, you could conceivably get one of >>those things to produce an output that would stay steady for at least a >>few seconds after a force is applied. But they will not respond >>indefinitely to steady force because they themselves have internal >>leakage. After all, there's no such thing as a perfect insulator. >> >>They're great for sensing mechanical vibration, that's for sure; and for >>picking up sound as well. But their piezoelectric nature renders them >>useless for measuring constant force. >> >>Dave D. >> >>>Dave Dilatush wrote: >>> >>>>David Harris wrote... >>>> >>>>>Does anyone know of a soucre of cheap strain gauges? >>>>> >>>>>What I want to do is measure the force applied to the coupler on my >>>>>model train. The plan is to measure the force and transmit it to a >>>>>readout station - via IR or rf. So, I need a way of measuring the force >>>>>-- any other ideas? (cheap is in :-) >>>>> >>>>Sad to say, I don't think there is any such thing as an inexpensive >>>>strain gauge, at least I've never come across one. >>>> >>>>This topic comes up every so often on the PICLIST and it seems there's >>>>never any really good solution. There ought to be, because there >>>>certainly is a need. >>>> >>>>I've been working on a low-cost, high-precision system for force sensing >>>>off and on as a "back burner" project for a while now and I'm making >>>>good progress; but it's going to be some weeks yets before I'm ready to >>>>post anything to the list. >>>> >>>>Dave D. >>>> >> >>-- >>http://www.piclist.com hint: The PICList is archived three different >>ways. See http://www.piclist.com/#archives for details. >> >> >> >> >> -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.