Analog Read/ Analog Ref Voltage range

I have a sensor that has a voltage range of 0-5 volts when connecting the Vout and Vref to my oscilloscope. Thus, I think "0v < Vout + Vref < 5V" is always true. However, when I look individually at Vout/Vref I have a voltage range of maybe +/- 10V which is not acceptable to the the Arduino Uno's A0 or Aref voltage range.

Does anyone have a suggestion on how to resolve this issue?

Can you post a picture of the wiring you used to measure your ranges? What is Vout and Vref at the sensor? Vout is probably the output voltage. Is Vref the same as the Vcc on the sensor?

My last question was due to using my oscilloscope improperly.

I now have a sensor that is powered by an external power supply. When hook up my Vout and Vref to my oscilloscope I get 0-5V depending on the sensor's reading. This is in the range of the Arduino Uno's analog pin.

When I hook my Vout and Vref to my Arduino Uno's A0 and Aref and connect my sensor's ground to my Arduino's ground I only get a reading between 4.28 and 4.32 volts. This configuration is shown in the attachment. When I leave the Arduino and sensor with grounded together and put the Vout and Vref back on the oscillascope the sensor will then only read from 4.9V to 4.8V.

It seems like when I ground my Arduino and sensor together my sensor no longer will read from 0 to 5 V. How can I resolve this issue?

Below is my code:

//Photoresistor Pin
int analogPin = 0;

void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
analogReference(EXTERNAL);
}
void loop() {
// put your main code here, to run repeatedly:
// read the raw data coming in on analog pin 0:
//analogReference(EXTERNAL);
int lightLevel = analogRead(analogPin);
// Convert the raw data value (0 - 1023) to voltage (0.0V - 5.0V):
float voltage = lightLevel * (5.0 / 1024.0);
// write the voltage value to the serial monitor:
Serial.println(voltage);
delay(250);
}

No link to the sensor or chip, and only bits of the puzzle.

One bad thing I can see. Sensor supply is 30volt.
If you share grounds, then 15volt of that (R5, R6) is going to the Aref pin of the Arduino.
Leo..

Define what you mean by "hook up my Vout and Vref to my oscilloscope"! Do you connect the base of your scope to Vout and the sensing needle to Vref? Measured voltage is always a difference between two levels. In your setup you should only measure from GND to a specific other point. And GNDs always have to be connected to enable the Arduino to measure a voltage level.