A-2

Current indication through A-2 and Sh-2

The A-2 works by measuring the voltage drop across the Sh-2 shunt. The main current passes through the shunt, and only a low-level measuring signal goes to the cockpit instrument. This is safer and more practical for high-current circuits. The scale has a center zero, so the pilot can see both current direction and current value. A positive deflection usually indicates battery charging or generator output. A negative deflection indicates discharge or operation from the battery when generation is absent or insufficient.

A-2 ammeter in aircraft DC systems

In an aircraft electrical system, the A-2 ammeter is normally connected to generator, battery or main DC bus circuits depending on the aircraft wiring diagram. It may work together with DC generators, starter-generators, voltage regulators, reverse current relays, contactors and battery circuits. The instrument itself does not regulate current and does not protect the network. It only gives visual indication. If the reading is incorrect, the cause may be in the shunt, signal wiring, terminals, generator circuit or the instrument movement.

Construction and installation of the A-2 instrument

The A-2 is a compact panel-mounted magnetoelectric indicator. Its external Sh-2 shunt is a separate calibrated current element designed for installation in the high-current line. The indicator receives only the measurement signal from the shunt. This separation is important during replacement: the ammeter and shunt must match by rating and voltage drop. Installing the indicator with a wrong shunt can give incorrect readings even if the instrument itself is serviceable.

Identification and ordering of A-2 with Sh-2

Before ordering, the installed ammeter and shunt markings should be checked against the aircraft electrical diagram or equipment list. Some requests require only the A-2 indicator, while others require the complete set with the Sh-2 external shunt. For correct selection, provide the aircraft type, circuit location, measuring range and whether the shunt is required. The product is also known under alternative designations A-2, А-2, Sh-2 and Ш-2.