Load cell, help

Question

I am using load cell, from here. Load cell specification are mentioned on the site. 5 wire coming out, its a 4 wire core shielded load cell.

I can't get the same voltage value from +Signal and -Signal.

###What I am using:

• Using arduino nano runs on 5 V.
• Supplied excitation voltage : 4.78 V ~(From USB).
• Have not grounded Shield wire.(floating)(required to ground?).
• Using AD622 ina, connected REF voltage = VCC.
• Using MCP3551 ADC, connected -Vin Voltage = GND.

###After checking from multimeter:

• (+ and - signal) from Load cell: reading: 2.45v. both giving the same with respect to ground.
• Ad622 6th pin, OUT pin, gives me 4.08v at 60-70 ohms. (using potentiometer).
• This OUT pin is attached to MCP3551 2nd Pin, .i.e +Vin.
• Readings are coming from MCP3551 are noise data i guess, in bytecode What else I can do to detect the fault.
• Below is code sketch

        
    #include 
    #include 
    
    #define SS 10
    
    float fRawData;
    MCP3551 MCP_ADC(SS);
    
    void setup(){
      pinMode( SS, OUTPUT );
       
      // initialize serial communication at 9600 bits per second:
      Serial.begin(9600);
      Serial.println("Setup done.");
    }
    
    float getRawData(){
      double fVar = 0;
      int i = 0;
      bool isReady = MCP_ADC.getCode();
      if( isReady ){
        Serial.print("Raw data:");
        Serial.print(MCP_ADC.byteCode, DEC);
        Serial.println();
        
      }
    }
    
    void loop(){
      getRawData();
    }

Where is the fault. What factor / point I should consider to troubleshoot this up?

---

^{simulate this circuit – Schematic created using CircuitLab}

Please check the schematic. Please ask me, if something is not clear in the picture.

Answer 1

So far I found 1 mistake in your design.

50ohm pot is too small (Rg value)

AD622 instrumentation amplifier gain range is 2 to 1000.

Your Ref pin at AD622 looks wrong

Typically that pin is connected to ground (for measuring positive voltages) or to Vcc/2 voltage for measuring positive and negative voltages.

Your Ref pin at ADC looks wrong

It should be connected to voltage reference (or Vcc).

Voltage at noniverting AD622 pin should be above or same as at inverting pin, because in-amp cant process negative differential voltage without double supply (with negative below GND).

I never had to do with such load cells, I have no idea what kind of output they have, but 4 wire connection looks like some bridge sensing.

For bridge sensing you may need negative voltage source to handle negative voltage from bridge. In-amp can't process any negative voltages at any pin if it has no negative voltage provided. I don't know if you want to measure also negative load... If you dont - maybe there is no need for negative supply.