Serial Handshake Help

Hello, I have two pressure sensors set up on a Uno that send their values via serial using a Xbee to a mega that receives the values and send them to a flow computer. The problem is that I do not know how to write a good handshake or some tag that identifies which value is from which sensor. Below is my sending unit code and my receiving unit code. Any help would be greatly appreciated. I have read several posts and examples but i still can't seem to apply any to my project.

Sending unit (UNO)

/* This program will read the Transducer Value from each sensor and send it to the xbee.
 * //This is for the Arduino Uno, Xbee Shield, and Xbee Pro S3 900Mhz 
 *  
 * - 8-2-2017 
 */
 
int sensorPin = 4;    // sensor positive lead // 1st transducer
int sensorPin1 = 3;   // sensor positive lead // 2nd transducer
// int PinOut = 9; // eneable for direct send to flow computer
float sensorValue = 0;  // variable to store the value coming from the sensor
byte outputValue = 0;


void setup() {

  Serial.begin(9600);
  
}

void loop() {
  
  sensorValue = analogRead(sensorPin);//Reads from the sensor transducer 1
  
  outputValue = map(sensorValue, 197, 1023, 0, 255);//scaling algorithm to create sendable value

 // analogWrite(PinOut, outputValue); // enable this line to send directly to flow computer
 
 Serial.write(outputValue); //Sends to the Xbee from 1st transducer
 
 delay(900);

 sensorValue = analogRead(sensorPin1);//Reads from the sensor transducer 2
 outputValue = map(sensorValue, 197, 1023, 0, 255);//scaling algorithm to create sendable value
 
 Serial.write(outputValue); //Sends to the Xbee from 2nd transducer
  
 delay(900); //Delay 

 
}

Receiving Unit (MEGA)

/* This program will read the Transducer Value from the xbee  and send it to the totalflow.
 * //This is for the Arduino Mega, Xbee Shield, and Xbee Pro S3 900Mhz 
 *  
 * - 8-2-2017 
 */
 

int PinOut = 9;
int PinOut1 = 10;
byte outputValue = 0;
float convertedValue;
void setup() {
  
  Serial.begin(9600);
  Serial1.begin(9600);
}

void loop() {
  
 // if (Serial1.available() > 0){
    outputValue = Serial1.read(); //reads value from the xbee from trans 1
    convertedValue = (float)outputValue;
    Serial.println("--------------");
    Serial.println(convertedValue);
    
    Serial.println("--- Tubing ---");
    analogWrite(PinOut, convertedValue); // send directly to flow computer for trans 1
   // Serial1.flush();
    delay(900);
    outputValue = Serial1.read(); //reads value from the xbee from trans 2
    convertedValue = (float)outputValue;
   
   Serial.println("--------------");
    Serial.println(convertedValue);
    
    Serial.println("--- Casing ---");
    analogWrite(PinOut1, convertedValue); // send directly to flow computer for trans 2
   // Serial1.flush();
 delay(900);
 // }
  
  //delay(1000); //Delay 

 
}

Simplest is

Serial.print("1"); Serlal.println(outputValue);

This will send as text; the first Serial.print identifies the sensor. You can check for “\r\n” to determine the end of the data and you know that the first character is the sensor so the remainder is the data for that sensor.

To make it compatible with the Serial input basics (example 3)

Serial.print("<1,"); Serlal.print(outputValue); Serial.print(">");

If you want to keep it binary, it’s a little trickier.