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Why is the PI damping resistor placed on the board and not at the coil?
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Because!
LOL! I think it was BB Sailer that suggested putting part of the required R on the board and using a Resistor in the Coil connector to the box to match and bal the coils .
That way any of the coils you build would be best matched with out board surgery.
Top end away from the coil is best because it takes care of the Capacitance of the Connecting Cable as well. -
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Why is a cable connected to a "fast" coil? This makes the network to operate as "slow" coil and decreases resistance of damping resistor for critical damping.Originally posted by bklein View Post
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As opposed to..? Is there a way to put the front-end on the coil without upsetting its behaviour?Originally posted by mikebg View PostComment
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Last I heard of , You need a cable to connect the coil to the Circuit.
The Cable has a C value to it.
If you want, you can put the front end of the circuit in with the coil but that makes problems of it's own.
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If you want four coils for different Jobs, Are you going to build a Front end for each one?
Sounds a bit Ruff to me.Comment
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Hi bklein,Originally posted by bklein View Post
you can not eliminate the coil leads capacitance, if you place the damping resistor at the coil. The coil leads form an additional capacitance, which is connected parallel to the coil. This connection is typically a low impedance path. Yes, there is also additional inductivity on the coil leads, which we won't take it into account.
From the point of capacitance, it doesn't matter, where you put the damping resistor.
But from other facts, it is better to place the damping resistor on the controller board:
1. Heat generation can be dissipated better (we do not want heat in the coil)
2. Required wattage and voltage of the damping resistor takes a large space (could cause response from the damping resistors)
AzizComment
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OR INSIDE CLEVIS TUBE
See this:Originally posted by AdrianM View Post
http://www.geotech1.com/forums/showp...8&postcount=15Comment
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You can put the damping R in the coil, but then every coil has to have the R, as opposed to just the detector.
The cable does have capacitance (or, more properly, a distributed RLC) and placing the R in the coil may result in some minor ringing in the signal that still requires a small amount of additional damping R in the detector. I don't recall this to be the case way back when I tried the damping R in the coil, but I wasn't looking at an aggressively fast coil and this may be a factor.
In short, there is no advantage (I can think of) to putting the R in the coil, and some minor disadvantages.
- CarlComment
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