twleiper@........ wrote: > > On Sun, 23 Jan 2000 13:29:11 -0800 barry lotzwrites: > >Hi > > I'm kind of entering this thread in the middle. ...continued. > > The problem with all this stuff is differentiating drift from legitimate > signal. In the example you cited, you simply have an indicator which > alerts the human (you) when attention MIGHT be required. After all, those > LEDs might be blinking due to a large quake. > > ... > Drift of +/- .5" can be ignored, and that range should be readily > achievable with a sensible and low cost design. > > HOWEVER, since not all are interested in such designs, let me tell you > how I WOULD do it if I thought it was worth the effort: > > It is logical to assume that, over a long period, a mechanically centered > boom will make as many excursions to the left of center as to the right. > There will be short term exceptions much as a bridge with double tolls > one way and toll free the other will carry "free" travelers who never > return, and paying travelers who always return via some other route. With > this in mind, I would simply put a "null" differentiator with adjustable > hysteresis (one quad OpAmp) on the "pen motor" signal (signal in your > design that is around 0 to +/- a volt or two) and have it clock a chip > (such as 74191)... the count total > (through use of divide by "N" counters), as well as the pitch and/or > gearing of the stepper you would have a simple and cheap method that > closely approximates the human operator. > > In normal operation the count may reach max/min in a couple days of slab > tilt, adjust the weight a little and then again a couple days (or weeks) > later. If you put the new piano in the room overhead and the boom swings > permanently to one side, the "X" minutes increment will eventually roll > over enough motor steps to correct for the condition. > > You want to try it? Go knock yourself out... Ah - it was fun ;-) I did roughly the same thing with a little BASIC STAMP computer (programmed in BASIC :-) http://www.parallaxinc.com/ which can be set to: - turn on LEDs - to do rough A-to-D (for the photo-transistors) - and programed to drive a stepper motor which drove something like a 36 to 1 gear box 'cus the adjustment screws take so little turning, and the torque of the stepper not very much. Added considerations are : - enable the actual adjustment only a fixed time of the day (to help prevent confusion about what might be happening} - short the pickup coil to - prevent massive signals from the electrical and mechanical noise from scaring you - damp the pendulum way above critical so it restores more smoothly after adjustment (I use resistive damping). It works - however, I still want to do a 3 axis force balance thing ;-) Cheers Ed Thelen _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>