Stuart Stevenson wrote: > Gentlemen, > The Gettys are three phase. > The encoders are 1000 pulses/rev giving 20,000 counts/in on the > linear axes and 2000 counts/deg on the rotary axes. > The Gettys are listed as 33 amp output. This I believe is 100% > duty cycle. I don't think this is peak rating. OK, then the bandwidth is not going to be much of a limitation. > I like the idea of using components that are as simple as possible > and having EMC do the work. > I will try to build an amplifier to use. If anyone has > suggestions/plans/gotchas please feel free to let me know. > I am trying to make a sow's ear cut parts. If I can get this > machine to position the tool tip to +/- .005 I will be very pleased. I > don't need speed I need reliability and strength. The strength is in > the cast iron. > This will let me cut parts to +/- .010 all day long. If I want > something closer than that I will put it on a different machine. Well, if you have some Servo Dynamics service/install manuals, they have some pretty detailed info on their analog front end. I can recommend the AD620 as a GREAT instrumentation amp. I used 3 of them in my velocity servo amp, one to read the command input, one for tach input and the last for the really hard part, reading the current by voltage across a sense resistor which is flying up to 80 V at 100 KHz rate. I used matched pairs of resistors to attenuate the offset by a fator of 10 or so, and the AD620 completely ignored the huge common-mode voltage and faithfully delivered the amplified voltage across the resistor. I was astounded at how well it worked.
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