Voltage Divider

What is the difference between using Ground or a reference voltage?

Thanks Again Marco

No difference; they're all wrong.

John

Why?

Show your math for determining the resistance ratios.

I have used a script into TI site.

{5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(32620),new

I have re-used the script and it has showed different values. R1 R2

12000 3000 30000 7500 Maybe I typed a wrong value.

Into the script there is the possibility to choose resistor scale 10, 100,

1000, ecc.

What is the difference, in this case between the 2 possibilities?

Many Thanks Marco

Input stage of voltage divider should be a strain gauge with signal conditioning to obtain 0 10v in single ended, or -10 +10 volt in differential.

Instead the output should be a voltage follower.

Which could be a good resistor configuration?

Many Thanks Marco

They're still wrong. There's not much data input validation on that script. You will need to conform to American practice and use "." rather than "," as the radix point. One exact possibility would be 39K & 13K

Loading on the 10V input and output impedance (about 10.3K in the example I gave above).

Best regards, Spehro Pefhany

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Do you have any additional specifications on the strain gauge such as its output impedance or allowable current range?

You want to choose resistor values such that they won't represent too low an impedance compared to that of the gauge in order to avoid loading it down.

I think you want the output to be 1/4 of the input, not 1/6. So: 7500:2500,

12000:4000, etc. (none of which are standard resistor values).

The amount of current that will flow into the input and the amount of additional voltage drop caused by current flowing out the output.

What is connected to the input and to the output?

You want the output to be 1/4 of the input.

So imagine a string of four equal resistors, +10 volts on one end and ground on the other. Call the voltages at the connections A B and C

A B C +10------r-------r-------r-------r------gnd

By symmetry, B os halfway from +10 to gnd, so Vb must be +5 volts.

Again, by symmetry, Vc must be 2.5 volts, which is what you wanted.

You can combine the left three resistors into 3R.

So R1 must be 3x R2.

John

The strain gauge specs don't matter; he has a signal conditioner. What he needs is the output current limit of the signal conditioner, which will be more than adequate for any of the total resistances that anyone has mentioned, including Spehro's correct one.

Since he intends to put a voltage follower on it, the same applies to the output. Any total resistance from ~2K to ~500K will be fine for just about any combination of signal conditioner and voltage follower I've ever heard of. Choose something convenient in the middle. Just keep in mind John's demonstration of 3R -- R, and make sure 4R is great enough to keep from loading your signal conditioner, which you should have specs for.

John Perry