npn/pnp sensors

[matt1e]

If the resistor only feeds 0v to terminal 4 then you can bridge it out and use three wire sensor.

yes I can confirm that the resistor only feeds terminal 4

OK, It looks like the original sensor was a simple n-p-n phototransistor, but because base was unconnected (no external bias w.r.t. emitter), it could be used to pull-up the voltage at T6.

For the new sensor, n-p-n output generally used to pull down a node (T6) to 0V in conjunction with a pull-up resistor.

So p-n-p output could be used to pull up a node (T6) to 15V in conjunction with a pull-down resistor - I think this is what you need..

Since you have the p.s.u./relay module apart, can you confirm a pull-down resistor on T6?

well I've atempted to trace terminal 6 the best I can, it leads directly to pin 2 of the socket at the top of the board then the track is obscured by the counter thumb wheels that also has components mounted beneath
and being a double side pcb I've lost track (pardon the pun)
If it helps the resistance reading between T6 and the negative rail when the module is re-assembled is 3.1k

 

[echoes]

well I've atempted to trace terminal 6 the best I can, it leads directly to pin 2 of the socket at the top of the board

Surely not the mains supply neutral 'pin 2'

If it helps the resistance reading between T6 and the negative rail when the module is re-assembled is 3.1k

Very plausible - a p-n-p output 3-wire sensor's worth a go IMO.

(You could get the n-p-n type to work, but not without modification and a circuit diagram and some faffing around - hardly worth the effort.)

 

[matt1e]

well I've atempted to trace terminal 6 the best I can, it leads directly to pin 2 of the socket at the top of the board

Surely not the mains supply neutral 'pin 2'

no mate its a socket that another pcb plugs into when you reassemble it

If it helps the resistance reading between T6 and the negative rail when the module is re-assembled is 3.1k

Very plausible - a p-n-p output 3-wire sensor's worth a go IMO.

this is what i'm hoping, a 3 wire PNP sensor connected
modified t4 = 0V> sensor blue
T5=+15V> sensor brown
T6= module input >sensor black
cable sheild> machine earth?

(You could get the n-p-n type to work, but not without modification and a circuit diagram and some faffing around - hardly worth the effort.)

I agree mate I knew I'd made a mistake rushing in and ordering it with out having a detailed look first, but it will be no probs changing it to a PNP type I haven't paid for it yet and I am on good terms with RS
many thanks to you and bernard for your input though, its not often I post on here asking for help!

 

[echoes]

No problem! Best of luck with it - it made a nice change from reading about 2 way-switching problems and cooker circuits.

 

[matt1e]

No problem! Best of luck with it - it made a nice change from reading about 2 way-switching problems and cooker circuits.

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[matt1e]

If the resistor only feeds 0v to terminal 4 then you can bridge it out and use three wire sensor.

Yes from your description it will be a PNP sensor you need.

The original circut of LED lamp and 220 resistor was putting about 60 milli-amps through the LED so provided the new sensor's operating ( supply ) current is less than 60 milli-amps it won't be overloading the power supply.

Ok managed to get to rs today and re-order so plumped for one of these , which is a PNP type with an operating current of 35mA so hopefully we'll be back up and running soon
Matt

 

[bernardgreen]

I hope you remembered to get the lead for it or a matching plug,

Been there when a buyer bought several sensors and assumed the leads came with them. "" If I buy a kettle it comes with the lead ""

Only we didn't laugh at 9 pm on site and un-able to test and commision.

 

[matt1e]

yup got a 2metre lead for it too mate

Matt