earth impedance

[SparkyTris]

under what practical circs might an earth impedance measured at DC be different to an earth impedance as seen by a 50Hz ac source?

 

[JohnD]

It usually happens when you weren't paying attention in class and can't do your homework.

 

[Taylortwocities]

 

[bernardgreen]

Prolonged application of DC and the resultant electrolytic action might result in the ground electrode becoming coated with a resistive layer.

 

[slippyr4]

Bernard, can you add "space cadet" to your sig?


I'll give the OP a clue to jog his memory ....

DC impedance is the same as resistance, but AC impedance is resistance and ???

 

[bernardgreen]

AC impedance is resistance and ???

inductance.

 

[slippyr4]

and ?

 

[slippyr4]

Prolonged application of DC and the resultant electrolytic action might result in the ground electrode becoming coated with a resistive layer.

That's wrong - any resistive layer, being resistive, would resist both AC and DC equally.

 

[bernardgreen]

That's wrong - any resistive layer, being resistive, would resist both AC and DC equally.

Copper Oxide Rectifier, resistive to both polarities but not equally.

 

[slippyr4]

Copper Oxide Rectifier, resistive to both polarities but not equally.

A semiconductor is not a resistor. You said "resistive layer".

 

[slippyr4]

inductance.

The right answer would have been reactance. I gave you the chance to redeem yourself by adding capacitance to your answer, but you didn't take it...

 

[John D v2.0]

I'm not even sure how many people are trolling, and how many people are being trolled! The op might have to use his text book after all...

 

[slippyr4]

 

[bernardgreen]

A semiconductor is not a resistor. You said "resistive layer".

This might be "old" (1943) but it refers to rectifiers as having non symetrical resistances but before the term semi conductor came into common use.

Copper Oxide Rectifier

With the use of the copper oxide rectifier in a recent receiver of the portable type, their popularity will possibly be revived for radio purposes, as in the days when they supplied rectified a-c for the fields of loudspeakers.

Any device which offers a high resistance to the flow of current though it in one direction, and a comparatively low resistance to the flow of current to it in the opposite direction, makes a good rectifier for an alternating voltage. This is the case of the dry contact rectifiers, such as the copper oxide type. The copper oxide rectifier is made in the form of a copper disk, coated on one side by a layer of copper oxide. The copper oxide is plated with nickel to allow good external circuit contact. The juncture of the oxide and copper offers a low resistance to the flow of current from the oxide to the copper, but a high resistance to the flow of current in the reverse direction. The detailed operation of this device is complex, but in general it involves the formation of thin films at the junction of the oxide and copper in which the molecules are so polarized that the transfer of electrons in one direction requires much less work than a similar transfer in the opposite direction.

Copper oxide rectifiers possess a definite breakdown voltage and breakdown temperature. If either critical value is exceeded, the rectifier will pass current freely in both directions. After the unit is cooled or the high voltage removed, it will immediately function again as though it had not been overloaded.

The copper oxide rectifier can be connected in either the half-wave rectifier or full-wave rectifier circuit.

The test for proper single disk operation is to impress a ½ -volt d-c across the disk in the conducting direction; then the current should read should read 0.5 amperes or more. By reversing the battery polarity a current of no more than 2 ½ Milliamperes should flow when 2 volts is applied to the disk in the non-conducting direction.

This was copied from the General Electric Company Electronics Department, booklet #175-3012A THE ABCs of RADIO (copyright-1943)

( my italics )

 

[slippyr4]

What planet are you on Bernard? Do you honestly, truly, think your comment was useful and correct and added to the thread?

You're justifying your tripe by digging up historical articles and playing games of semantics.

Know when to stop.