Help to read MB7078 XL-MaxSonar-WRCA sonar values

I'm using this IP67 sonar: MB7078 XL-MaxSonar-WRCA with Arduino Mega (i tried to use Arduino UNO, too, but it didn't solved the problem). Here you can find the sonar datasheet: http://www.maxbotix.com/uploads/MB7068-MB7078_Datasheet.pdf

I tried to use both the analog sonar output and the PWM one but in both cases i'm not able to read correct values because it always prints random numbers or fixed ones. For example, if i use the analog output and i tried to read the analog value i always have something like sensorValue = 114 and it never changes.

int sensorPin = 0;    // select the input pin for the potentiometer
int sensorValue = 0;

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(sensorPin, INPUT);  
  Serial.begin(9600);
}

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);    
  Serial.println(sensorValue);
  delay(125);             
}

I do not think the sonar is broken because i've bought in total three sonars (same model) and all of them do not output correct values. I'm sure i'm not doing it in the correct way. Can you help me, please?

I connect the Vcc and GND to Arduino and the analog output to analog pin 0 without using a resistor or a capacitors to avoid noise.

any ideas? :(