instantiate an object within another object?

I'm not sure what the terminology is called.... I am trying to instantiate an object within another object.. I am getting these errors:

Uncaught Error: Field or method does not already exist, and can't
create it on undefined at line 2 col 10
this.ph.updateResTemp(tempCompensation);

      ^ in function "getPhValue" called from line 2 col 22   bot.getPhValue(90.5);
                  ^

Code:

I2C1.setup({scl:b6, sda:b7});

Serial4.setup(9600, {tx:C10,rx:C11});

function s7s (theAddress) {
  this.address = theAddress;
  this.displayTable = {
    "Clear" : 0x76,
    "dp"    : {
      "cmd" : 0x77,
      "location"   : [
          0b00000001, //Digit 0
          0b00000010, //Digit 1
          0b00000100, //Digit 2
          0b00001000  //Digit 3
      ]
    }
  };
}

s7s.prototype.writeValueToDisplay = function () {
  var toChar = "";

  var a = this.address;
  var clrCMD = this.displayTable.Clear; //Display clear command
  var dpCMD = this.displayTable.dp.cmd; //Decimal point command
  var dpLocation = this.phDisplay.displayTable.dp.location; //Decimal point location map

  I2C1.writeTo(a, clr); //Clear display
};

function Sensor (theType, theAddress) {
  this.type = theType;   //i.e. PH
  this.address = theAddress;  //i2c Address
  this.sensorResult = 0; //Store sensor result
  this.cmdTable = {
    "Calibrate" : {  //List of Calibration commands and timeout value.
      "clear" : { "cmd" : "Cal,Clear",      "wait" : 300  },
      "mid"   : { "cmd" : "Cal,mid,7.00",   "wait" : 1300 },
      "low"   : { "cmd" : "Cal,low,4.00",   "wait" : 1300 },
      "high"  : { "cmd" : "Cal,high,10.00", "wait" : 1300 },
      "query" : { "cmd" : "Cal,?",          "wait" : 300  }
    },
    "Information" : {  //Device Information
    },
    "LED" : {  //Enable / Disable or Query the LEDs
      "L0" : { "cmd" : "L,0", "wait" : 300 },
      "L1" : { "cmd" : "L,1", "wait" : 300 },
      "L?" : { "cmd" : "L,?", "wait" : 300 }
    },
    "Reading" : {  //Takes a single reading
      "R" : { "cmd" : "R", "wait" : 1000 } //Takes a single temperature compensated reading
    },
    "Serial"      : {  //Switch back to UART mode
    },
    "Sleep"       : {  //Enter low power sleep mode
    },
    "Status"      : {  //Retrieve status information
    },
    "Temperature" : {  //Set or Query the temperature compensation
      "T"  : { "cmd" : "T,19.5", "wait" : 300 },  //Where the temperature is any value; floating point, or int, in ASCII form
      "T?" : { "cmd" : "T,?",   "wait" : 300 }  //Query the set temerature
    },
    "Factory"     : {  //Factory reset
    },
  };
}

Sensor.prototype.getSensorType = function () {
  return this.type; //Get Sensor type
};

Sensor.prototype.getSensorAddress = function () {
  return this.address; //Get Sensor address
};

Sensor.prototype.getSensorReading = function() {
  var a = this.address;
  var d = I2C1.readFrom(a, 7);
  return d;
};

Sensor.prototype.getSensorResult = function () {
  var a = this.address;
  var c = this.cmdTable.Reading.R.cmd;
  var w = this.cmdTable.Reading.R.wait;
  var that = this;

  I2C1.writeTo(a, c);

  setTimeout(function (e) { callback(that.getSensorReading()); }, w);
};

Sensor.prototype.storeSensorResult = function () {
};

Sensor.prototype.updateResTemp = function (temp) {
  var a = this.getSensorAddress();
  var c = this.cmdTable.Temperature.T.cmd;
  var w = this.cmdTable.Reading.R.wait;
  var that = this;

  Serial4.print(a + " " + c + "\r\n");

  I2C1.writeTo(a, c);
  setTimeout(function (e) { that.getSensorReading(); }, w);
};

function processData () {
  //Sensor Objects
  var ph = new Sensor("ph", 0x63);
  var ec = new Sensor("ec", 0x64);

  //Sensor Displays
  var phDisplay = new s7s(0x71);
  var ecDisplay = new s7s(0x72);
}

processData.prototype.getResTempValue = function () {

};

processData.prototype.getRoomTempValue = function () {

};

processData.prototype.getRoomHuminityValue = function () {

};

processData.prototype.getPhValue = function (tempCompensation) {
  this.ph.updateResTemp(tempCompensation);
};

processData.prototype.getEcValue = function (tempCompensation) {

};

Serial4.on('data', function (data) {
  Serial4.print(data);

  var edisonData = data;
  Serial4.print("Edison sent: " + edisonData);

});

var bot = new processData();

setInterval(function (e) {
  bot.getPhValue(90.5);
}, 3000);