# A better formula for Silonex LDR's

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#### jackinnj

I plugged in about 100 data points for Current (x) and ON-Resistance for the Silonex NSL32SR3 Attenuator -- the errors for the very low currents are close to zero --

An externally hosted image should be here but it was not working when we last tested it.

This is much better than the results using the Silonex equations.

Here's the equation - ymmv:

An externally hosted image should be here but it was not working when we last tested it.

#### AndrewT

Can I assume that e5 = 10^5?

#### kristleifur

Can I assume that e5 = 10^5?

Yep, that is the notational custom - as I know it at least

#### jackinnj

I liked it because there is no exponentiation, and only a few terms. The equations with multiple terms offer no improvement in accuracy. A stepwise approximation can probably resolve the low ohms error.

#### udailey

How many different LDRs is this based on John? One with 100 measurements or several with several measurements? Yeah, their datasheet is nothing close to real use.
Uriah

#### Blues

Nice one Jack...btw, x=current in uA. Actual testing/matching is still the way to go but it can serve as cross reference.

#### Blues

On second thought...your formula is pegged down at 47R...it certainly can go lower

#### jackinnj

On second thought...your formula is pegged down at 47R...it certainly can go lower

the very low resistance points are the insertion loss.

do the math for a 0.5dB 100K+100K attenuator -- you need accuracy in the tens of picoamps in the part of the range where we do most of our listening.

#### Blues

On second thought...your formula is pegged down at 47R...it certainly can go lower

And can also go much higher, I might add, and controllable too.

the very low resistance points are the insertion loss.

do the math for a 0.5dB 100K+100K attenuator -- you need accuracy in the tens of picoamps in the part of the range where we do most of our listening.

Not quite...with a more precise power delivery "engine" . Listening range is mostly in 10s of uA to 100s of uA. With this design working range is from <1uA thru 10s of mA.

I'll probably start a thread...

#### jackinnj

Several forms of equations will work -- but I have to say that the Silonex devices are all over the place!

Here's my setup -- using an LTC or ADI difference amp allows stable current in the picoAmperes:

An externally hosted image should be here but it was not working when we last tested it.

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