[ARC5] RE meters

[J. Forster]

That's not a surprise. The meter is actually linear, but the scale is calibrated
to correct for the non-linearity in the current sensor.

The thermocouple unit has a series resistor in the RF circuit (The current
transformer just isolates and scales.. it is linear). The power dissipated in
the R of the sensor is current squared x R  (I**2 x R) and is non.linear.
Assuming the heat losses in the thermocouple assembly are by conduction only
(good approximation) the temperature rise will be proportional to the power
dissipated, or the square of the RF current. The thermocouple produces a voltage
proportional to temperature, and so is linear.

So, in short, the non-linearity is due to the heating effect of the RF current,
which is proportional to the current squared. The scale corrects for this.

-John

philip wrote:

> One thing I do know about the antenna relay meter is that
> it is nonlinear. The meter movement that is.