Non destructive testing using dc source and hall sensors

I am working on non destructive testing using hall sensors dc source and i am facing problems in the measurement of voltage.Typically the input voltage is measured input and ground and output voltage between ground and output.The output voltage should be half of input voltage but i am getting it only at one sensors.The voltage of second sensor is not constant.I isolated both the sensors and tested it but it shows the same result.There might be some manufacturing defect in the sensor .I will be using new pair of hall sensors which should be good but i may experience similar problem as in the last setup.There are two hall sensors(a1301-02) (a1308-9) which are used separately in two devices Please refer the screenshots for more information.I wanted ways to reduce voltage fluctuation.There is no connectivity problem nor there are any loose connections.The hall sensor is mounted on a bobbin which encloses steel core and copper coil is wounded on the bobbin.
The schematic diagram for the circuits