Voltage across alarm pair

[Europlex]

Whoops, you're right, nearly it's an 8R, I was looking at the 8, too many panels, too many same but different PCBs!

As an aside, I don't really want to get into this one but, if it's any help or hinderance, I've just put my meter across ct7 of an old Scantronic 9100 and guess what 13.43v (but will not light an l.e.d.) - work it out boys

 

[Spark123]

The volts are there when there is no current flowing in the circuit and can be measured using a high impedance volt meter? An LED requires something like 20mA to light, however owing to the design only about half a mA can flow in the circuit?
From looking at the R8 PCB each zone appears to be assembled as such:

The supply is a little bit greater greater than 12v but you get the idea. The IC is the large IC in the photo, all the zones go back to different legs on this IC.

 

[securitywarehouse]

Not wishing to get dragged in either lol

But
On a 12v or 5 v panel there is a source and an input, in basic terms the left hand terminal gives 0v and the right hand terminal is expecting to recieve 0v. This (via filtering) is connected to the input stage of the processor, but the processor needs to be able to tell the difference between 0v and not 0v. ie 0v = closed circuit. The easy way to do this is to use a pull up resistor (say 20k) between 12v and the input. This then 'pulls up' the voltage from 0v to 12v when the circuit is open.

This is how you can see 12v across a circuit but no current is available as its purly to control logic levels. MOst panels work on <1.6v = 0 and > 1.6v is 1

But this depends on the IC type.

Hope this helps....

 

[securitywarehouse]

beaten to it lol

 

[saxondale]

no i mean normally as in if the NORMAL reading is 13v what is the tamper return reading if its OC (clue - it isnt 0v)

 

[Europlex]

Not wishing to get dragged in either lol

But
On a 12v or 5 v panel there is a source and an input, in basic terms the left hand terminal gives 0v and the right hand terminal is expecting to recieve 0v. This (via filtering) is connected to the input stage of the processor, but the processor needs to be able to tell the difference between 0v and not 0v. ie 0v = closed circuit. The easy way to do this is to use a pull up resistor (say 20k) between 12v and the input. This then 'pulls up' the voltage from 0v to 12v when the circuit is open.

This is how you can see 12v across a circuit but no current is available as its purly to control logic levels. MOst panels work on <1.6v = 0 and > 1.6v is 1

But this depends on the IC type.

Hope this helps....

EXACTLY !

 

[saxondale]

Whoops, you're right, nearly it's an 8R, I was looking at the 8, too many panels, too many same but different PCBs!

As an aside, I don't really want to get into this one but, if it's any help or hinderance, I've just put my meter across ct7 of an old Scantronic 9100 and guess what 13.43v (but will not light an l.e.d.) - work it out boys

right - so you now see you dont HAVE A VOLTAGE across the terminal, you have an implied reading but its pointless for fault finding


reminds me of the old "if the witch drowns she was innocent"

 

[Spark123]

Why is it pointless for fault finding? And what is my fluke reading when set to volts, if not voltage?

 

[saxondale]

Why is it pointless for fault finding? And what is my fluke reading when set to volts, if not voltage?

OKAY OKAY so I didnt look where the little bobbly bit was pointing LOL now get over it

problem with looking for 13v to prove an open circuit is you have to take reading disconnected from the board for them to be meaningful for exactly the reason were arguing this point - there false readings

and what happens if you dont get 13v ?

what if (as has happened in this case with garrymum) the fault is a ground voltage thats been introduced onto the cable by a nail etc (the long fabled short between poles)

what if its just a high resistance ?

your going to do the maths and work it all out using ohms law?

totaly the wrong thing for trying to work out a wiring fault

 

[Spark123]

If you disconnected the wires and didn't get 13v it would imply a panel fault though, wouldn't it?

 

[securitywarehouse]

if you disconnect the wires you might get 5v or 12 or nothing. Its not really a test as such as it would depend on panel and polarity etc.

The wires should on a double pole circuit give <100 Ohms if closed >200k if open.

Just measuring the panel zone connections with nothing connected isnt an ideal test, the only sure test to test a panel is to link it (either short or resistor depending on type) and see if the diagnostics show the correct status (ie closed)

You might want to meter between 0v and the disconnected wires to ensure there is no voltage on the circuit coming from the sensor as it should be clean switched

 

[saxondale]

If you disconnected the wires and didn't get 13v it would imply a panel fault though, wouldn't it?

but were not testing the panel -were looking for the faults on the cable

 

[Spark123]

How would you know if the fault is on the cable or with the panel?

 

[saxondale]

How would you know if the fault is on the cable or with the panel?

the O/P claimed the panel didnt trigger although the PIR lighted up - just remove the circuit cables from the panel

if it triggers the faults on the cable

if it doesnt trigger then check the proggraming

experiance (and the fact she`s been nailing) says that it wont be a faulty panel

 

[Spark123]

Why not check the voltage with it connected and disconnected? About 0v with it connected and open circuit voltage with it disconnected or operated? This would have pointed towards the wiring as opposed to the panel.