Indeed, too simple. What is the output impedance and voltage compliance of the sensor?
For instance is it a genuinely constant current output with rail-to-rail compliance? Likely not,
it probably is a voltage source into a series resistor already - in otherwords it may be
designed to work with a particular meter with a particular resistance (usually in the 100's to
1000's of ohms range for that sort of analog meter).
Get out the multimeter and measure the output voltage.
Then place the multimeter in series with 1k and measure the output current and compare....