The instrument is designed to measure with high precision voltage the vehicle battery and for other applications where you want to control voltage in the range of 10...15 V with an accuracy of 0.01 V.
The voltage is completely discharged, discharged and fully half charged battery is equal to 11.7; 12,18 and 12,66 In respectively. For to measure the voltage with such precision, or need a digital voltmeter, or an arrow with a stretched scale.
The circuit shown in the figure, it enables any of the microammeter scale 50 or 100 μa to make a voltmeter with a scale measuring 10...15 V.
The voltmeter is not afraid incorrect wiring (polarity scrambling) to the circuit being measured (in this if the readings do not correspond to the measured quantity). For protection of the microammeter RA1 from damage during transportation is the switch S1, shorting the conclusions of the measuring device, which prevents fluctuations of the arrow. The instrument PA1 with mirrored scale type M1690A (50 µa), but an other. Precision Zener diode VD1 (DD) with the last letter of any in the designation. It is better to use multi-turn potentiometers, for example, R2 type SDR-36, R5 type SP5-2B. To configure'll need a power supply with adjustable output voltage 0...15 V and exemplary voltmeter (preferably digital).
Connect the power supply to the terminals X1, x2 and gradually increasing the the voltage to 10 V, the resistor R5 achieve "zero" cursor position device RA1. Thereafter, the supply voltage is increased to 15 and In resistor R2 sets the arrow on the limit value of the scale. On this the setting can be considered finished.
The device can be done multifunctional. Connect the findings of the microammeter to the scheme through the disk toggle and PN get a normal voltmeter (picking up a series resistor), and the tester circuits and fuses.
The device can be supplemented by a circuit for measuring AC line voltage with a scale of 200 to 300 V.