permitivity

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About permitivity

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  1. 24VDC guard door circuit

    Thanks for the replies: 1. I can not up the voltage of the power supply as it is being used for other things too. 2. The relay is a AB 700S relay. It has the smallest power consumption compared to other industrial relays. 3. I'm using a cable, so the gauge is not easily changed. 4. Weird, but the spec sheet on the relay doesn't list minimum pull in voltage - only power consumption. Is there anything wrong with my math?
  2. Hello, I have a really long 24VDC guard door circuit, and I went and calculated how much votlage drop there would be and whether there is still enough voltage at the end of the run to pull in a relay. Could someone look at the why I calculate this to see if it's right? Run: 1900ft of 18 guage wire: <0.00751ohm/feet * 1900ft = 14.3ohms> Relay: 24VDC coil, rated at 6.5W power consumption, so that's about 0.28A. So coil has 24V/.28A=86ohms Total resistance: 24V/ (14.3ohm+86ohm) = .24 amps. So I can expect .24amps on the wire, which is slightly less than the .28A needed to pull in the coil. Does that mean I wouldn't be able to use this relay, or might have to go 120VAC? How much wiggle room is there on these ratings? The relay doesn't list a minimum, simply the rated coil energy. Thanks,
  3. relays

    Hi, On some relays, like Allen-Bradley relays, they mention it has an "Integrated Diode". Does that keep noise off the line when the coil energizes? Thanks, P
  4. Hello, I am new to this forum. Do input cards like <AB 1394 discrete input> carry current in the input signal wire? For example, if you have a limit switch, at one end is the 24V DC supply, and the other end is connected to the input card. When the swtich is closed, does current (and how much?) actually flow through the wire, and the input card sees "ah, 24V, I see signal"? I'm not sure if the input cards act like volt meter - they just sense voltage? Is there actually any current flow? I tried the data sheets, but I couldn't find much. Thanks, Eric