1k pull up resistors

Jimster
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1k pull up resistors

Postby Jimster » Thu Mar 27, 2008 3:42 pm

Hi There, no doubt this will be my first of many questions.

I undertand that many sensors on the DL1 require a 1k pull up resistor, what wattage should I be using?

Thanks
Jim

tristancliffe
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Postby tristancliffe » Thu Mar 27, 2008 6:00 pm

I'd have thought anything over 0.25W would be fine. I think 1W are probably the most common...

Most sensors are in the range of 0.01 Amps, at 5V (call it 12V just in case). Power = IV = 12*0.01 = 0.12W.

Power also = RI^2 (resistance x current squared) = 1000 x 0.01 x 0.01 (worst case remember - actual currents are almost certainly a lot less!) = 0.1W...

The ones that come with R-T sensors are very small - probably 0.25W. The ones I use are what Maplin had on the shelf that day, which were 1W...
Monoposto 2000 - Reynard 883 Toyota

Jimster
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Location: Bridgend, South Wales
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Postby Jimster » Thu Mar 27, 2008 7:41 pm

Great thanks, I've ordered some 1w resisitors

faraday
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Postby faraday » Fri Mar 28, 2008 2:36 am

Either way, it's not going to break the bank (for a change), but unless the resistor is to convert a current loop style sensor to a "voltage" style, there is no need for the expense of high tolerance resistors.

If you're using a sensor manufacturer's calibration data, with OHM's law applied to correct for your resistance, then definetely spend the extra pennies.

Has anyone out there built their own temperature sensor?
I recently made an under-plug CHT sensor with a Pt100 RTD. I was probably over-concerned about too much current and self heating, so at this stage my fixed Rs in the voltage divider are too high, giving insufficient resolution for the 12 Bit A-D.
Good thing we aren't stuck with real el cheapo 8 Bit!

Turby
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Joined: Thu Nov 17, 2005 2:28 pm

Postby Turby » Fri Mar 28, 2008 2:17 pm

I successfully built my own dual channel thermocouple amplifier a couple of years ago which I use to measure temps going into and out of a chargecooler. Based around a pair of AD595's and a few other discrete's such as resistors and capacitors.

faraday
Posts: 267
Joined: Sun Feb 25, 2007 1:18 am

Postby faraday » Fri Mar 28, 2008 3:27 pm

I am a mechanical engineer with very basic electronic knowledge, so you're racing ahead of me. Faraday is my ginger cat's name. He doesn't mind experimenting.
Before I took the time to contribute to the forum, I noticed some of your posts that indicated you had some useful skills and knowledge in several areas.
They might be in cold threads now. Nevertheless, over the next few days, I'll try to find them and try raise your attention if I need further enlightenment.

Thanks

Turby
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Joined: Thu Nov 17, 2005 2:28 pm

Postby Turby » Fri Mar 28, 2008 7:56 pm

Probably best to email me...


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