Trouble with Z zero plate

[gdayers]

I just received and installed a new zero plate for my 2nd 'bot. Both my machines are older PRTs. Unlike my other plate the new plate has an aligator clip on it. The only install instructions I could find for this type of plate was under instuctions for the Alpha PRT. Those instructions say to hook the clip to the bit. The input 1 light goes on as soon as the clip is hooked, before the plate even contacts anything. Is this setup only for the alpha machines or am I doing something wrong. I just recently swithched my old plate from this machine to the other, and it worked just fine then.
Gregg

[paco]

I too assume that this setup is specific for the Alpha since it closed the the system "differently"... Personnaly I clip this wire (the one with the alligator clip) at the router body permently... so I can use it as on PRT wihtout having to clip it each time...

[richards]

The Z-zero plate acts like a simple switch. One side of the switch is always connected to signal ground (the side with the alligator clip) and one side is connected to a digital input (the actual metal plate).

With the power off, use an ohm meter to see which of the connecting points in the control box is ground and attach the wire running from the alligator clip to that point. Attach the wire running from the Z-zero plate to the other control board input connection.

On my Alpha, I leave the alligator clip attached to one of the bolts holding the controller box to the steel frame. (There is good electrical conductivity through the case of the router, making a connection to the bit unnecessary with my Porter-Cable router.)

If it's any consolation, my Z-zero plate also did not work until I reversed the connections.

[fleinbach]

I have a Prtalpha 120 with a 3 HP Colombo spindle motor. When I first set it up I was told I would need the alligator clip. Well I have never used one and so far everyting zeros flawlessly. I never had one anyway since I kept the old zero plate when I sold my old PRT

[beacon14]

The clip is only needed when the router bit is isolated from ground due do the design of the spindle. With PC routers the bit is in electrical contact with the body of the router, so as long as the router mount doesn't isolate the router from the machine the clip isn't needed.
However, if the input light goes on as soon as you touch the clip to the router bit (or machine frame), then it sounds like the zero plate and clip leads are reversed inside the control box, as Mike explained. If it is hooked up correctly, touching the zero plate to the machine frame (in an unpainted spot) or to the router bit should complete the circuit and activate the input switch, and touching the clip to anything except the zero plate should do nothing.