Use Hall Ammeter of you can measure positive current and negative current. You can measure the current of +VCC/-VCC/GND .Use Hall Ammeter measure any DC current unlimited,for that the Hall Ammeter of measure is isolated. This design allows system designers to monitor any current path without breaking or changing original-system layout at all. Working current: 7-15mA Power supply: DC 5-120V Sensor hole diameter: 20mm Operating temperature: -4- 140(-20-60) Name:Hall current voltmeter Accuracy:+ - 1% Resolution:0.3A Type:Hall Ammeter Voltmeter Style:LED Digital Isolated meter Output Type:DC 5-120V Model Number:dc Voltage Current METER Default wire 0.15M. Instructions: (1) Access Power Supply range 5V to 120V (2) Use electric wire by pass it through the hole of hall current sensor to measure passing current. Key Instructions: Short , when the time less than 2 seconds of key. It switching Hall Ammeter for there mode: [1]Current voltage in turn display mode. [2]Single current display mode. [3]Single voltage display mode. How to switching mode? (1)Short key of the back,the LED display "A",that means now in single current display mode. (2)Again short key of the back,the LED display "A U",that means now in current voltage in turn display mode.(Note:when display current the LED display flashing,and display voltage it not.) (3) short key of the back,the LED display "U",that means now in single voltage display mode.(Note:when measure the voltage it was the power supply voltage of Hall Ammeter) Long ,when the time 2S of key. The LED display "" that it clear the current. Measurement Range:+ -400A Colour:Black & Gray Material:Plastic Package Contents: 1 set * Hall current voltmeter Only the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.