Uwe Langmesser wrote in message ...
Is there a simple relationship between a meters internal resistance and its
sensitivity (ohms per volt).

No.

Maybe this is trivial but I don't see it.

Not trivial at all. The internal resistance of a meter depends on the
type of meter (D'Arsonval, moving iron, electrodynamometer, etc.) and
its design.

As a simple example, imagine two identical 0-1 mA D'Arsonval meters.
Now replace the springs in one of the meters with new ones that
require more force. The meter with the "stronger" springs will need
more current for fullscale deflection even though it has the same
internal resistance.

---

There *is* a relationship between a milliammeter's fullscale reading
and the ohms-per-volt when it is used with a series resistor to make a
voltmeter.

Ohms-per-volt = 1/current for full scale deflection (in amps)

So, when used with the appropriate series resistor(s):

a 0-1 mA meter will give 1000 ohms-per-volt
a 0-100 uA meter will give 10,000 ohms-per-volt
a 0-50 uA meter will give 20,000 ohms-per-volt

etc.
73 de Jim, N2EY