Arfa Daily wrote:

"M" wrote in message
...
Where can I find a web page that describes resistor value designations?

I have a schematic that calls out a resistor value of 4K74. Is this 4.7K?
If so, what's the last "4" for? If it's not 4.7K, what is it?

Further, there are values of 681R (681 ohms?), and 27K4 (? ohms).

Did the Google thing but never found a formal chart.

TIA

Mike


It's common in Europe to see the multiplier - in this case "k" - placed
where the decimal point would be to avoid specks of fly**** on a page
looking like a decimal point. So, a resistor designated 4k74 is the same as
4 point 74 k ohms. This may appear to be an 'odd' value of nearly, but not
quite, the standard 4.7k (4k7) but may well be correct if the resistor is to
be found in some precision circuit such as an opamp based filter with a
specific cutoff frequency, or instrumentation amplifier requiring a precise
gain figure. Such resistors are often calculated to this level of precision,
and require to be made up from two or more values from one or several of the
'preferred' (standard) ranges of resitor values. 27k4 is 27.4k.

"681" is unlikely to be an 'actual' value of 681 ohms. If it is a surface
mount resistor that is being specified, it is probably 680 ohms, as these
resistors are physically marked like this. It's the equivalent of marking
them with coloured bands, but using the actual figures instead. Thus, the
third digit is the equivalent of the multiplier band on a coloured stripe
resistor. In your example 681 would mean "6" "8" (number of noughts) "1" or
680 ohms (may also be shown as "680R" using the system in the first
paragraph)

Just to confuse you, a resistor marked "680" in the surface mount scheme,
will be 68 ohms, that's
"6" "8" (number of noughts) "0" This could also be shown as 68R in the other
scheme. A 0.47 ohm resistor would be shown as "0R47". A 100k resistor
would be shown as "100k" (!!) and a 3.3 meg as "3M3" In surface mount they
would be marked "104" and "335" respectively. Just for completeness, caps
are often shown using the same schemes. So a cap shown on a schematic as
"4n7" will be 4.7 nanofarads, or 4700pf. It will quite likely be physically
marked using either resistor colour code stripes - yellow, purple, red - or
the equivalent numbers in the same way as the surface mount resistors thus
"472"

Arfa


Here is a javascript for the two character codes on SMT capacitors:
http://home.earthlink.net/~mike.terr.../SMD_caps.html

I also have a three digit (5%) and four digit (1%) javascripts for
resisitors, and the old three and six dot Micamold cpaacitors that I
will make availible when I have more server space.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida