Input convertion from 13V to 5V

Good day to you all.
I need to read the analog output of a Vacuometer (baratron 127A MKS) with my Arduino.
The problem is that the output of the instrument is on a 10V scale and the only solution i found was to use 2 equal resistances in series to get a proportional voltage of 5V .
I am having a lot of misreads that oscillate up to two orders of magnitude from the control value of another vacuometer.
Where is coming this noise from?
Do i need to insert a capaitor somewhere to get better results?
Do i need just to create a mean of more AnalogReads?

Thanks for your time

Davide Lamberti

FIR_PRES_1Torr_127A_MAN.pdf (141 KB)

Page 15: "The ground of any external power supply and readout should be the same as the sensor ground (chassis ground), to minimize any possible ground loops which can affect the performance and stability of the system."

The output demands a load impedance of 10k or greater, suggesting use of say
10k +10k divider (20k load to the meter). You could add 10nF on the output to reduce

If you have ground loop issues then a differential reading might be better - use 2 voltage
dividers, one for signal and one for signal ground and subtract the two readings (however
that isn't quite enough if the signal ground dips below Arduino ground - you'd want to reduce
the "gain" of the divider to less than 0.5 and add a small offset with a high-value resistor to +5V, bringing the signal to, say, the range 0.5V to 4.5V on the Arduino pins.


Noise could come from different places.
Couple quick check where is coming your noise:

  1. Check your power supply for ripple voltage with oscilloscope
  • Datasheet specify for power supply line maximum 20mV peak-to-peak ripple and noise voltage.
  1. Check your output signal for ripple voltage with oscilloscope.
  2. Use good quality screened cable for connection and make sure it is short as possible.
  3. If you use switch mode power supply than try to change to analogue power supply.