Re: pig power control

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Wire the Estop as a normally closed circuit (that is, closed is Enabled)...
if the estop wire breaks, or someone, in a panic, yanks the switch and cable
out of the attachment, or pulls the plug loose (yes, these have all
occurred), then the system shuts down.

Generally, you'd wire it so that the coil of the main contactor going to the
big load (i.e the pig) is wired in series with the Estop circuit, and the
circuit that powers the coil is downstream of the Estop. Once you hit the
Estop, the control logic is powered off, and can't be repowered without some
explicit action (other than releasing the Estop button)

Don't wire the Estop circuit as a momentary contact kind of device (i.e. it
sends a pulse to toggle something).. you want it to latch... A lot of
commercial pushbuttons intended for Estop use (i.e. red mushroom head,
Emergency stop labelling) are set up for latching.. you push it, and it
sticks.. you have to turn it to release it back to the operable state.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, November 13, 2002 10:34 AM
Subject: RE: pig power control


 > Original poster: "Mccauley, Daniel H by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 >
 > Here some info for starters:
 >
 > 1.  Very large variac or stacked variac (PowerStat 1256D 240VAC, 28A are
 > good for smaller pole transformers)
 >
 > 2.  MAINS Contactor for output enable
 >
 > 3.  Separate contactor for E-STOP, Interlock, Key Safety Switch which
powers
 > MAIN contactor
 >
 > 4.  Fusing / Circuit Breakers (to protect the wiring and prevent fires)
 >
 > 5.  Analog voltage / current meters (old analog simpsons work great)
 >
 > 6.  External E-STOP circuit.  So in the result of serious injury, someone
 > entering the room or area can safely turn off
 > power from a distance.  This switch should be easily visible and labeled.
 >
 >
 >
 > Remember, the controller isn't a trivial thing.  Always remember safety is
 > number one concern here.
 >
 >
 >
 >
 >
 >
 > I need information on controling a pig?   if I was to get my hands on a
 > PIG  how would I construct a controller for it?
 >
 >