A-2

Aircraft ammeter A-2 with Sh-2 shunt

The A-2 is an onboard magnetoelectric ammeter used with an external Sh-2 shunt for measuring DC current in aircraft electrical systems. The instrument is installed on the cockpit panel, while the shunt is mounted in the power circuit outside the indicator. This layout allows the crew to monitor generator load, battery charge and discharge current without routing heavy power cables directly to the instrument panel. The A-2 is used on aircraft, helicopters and special ground equipment with DC electrical networks.

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.

Product Type: Aircraft DC ammeter with external shunt
Function: Visual indication of DC current in aircraft electrical systems
Application / Where Used: Aircraft, helicopter and special ground equipment DC power networks
System / Installation Area: Cockpit instrument panel / DC power circuit with external shunt
Part of System / Included in Set: A-2 ammeter with Sh-2 external shunt
Measurement Range: −50 A to +500 A
Scale Division: 25 A
Shunt Type: Sh-2 external shunt
Shunt Rated Current: 500 A
Voltage Drop Across Shunt: 75 mV at maximum current
Accuracy: ±2.5% of the sum of measuring limits
Operating Temperature Range: −60 to +50 °C
Vibration Resistance: Up to 1.5 g continuous vibration
Shock Resistance: Up to 10,000 shocks with 4 g acceleration
Indicator Dimensions: 47.4 × 47.4 × 79 mm
Indicator Weight: 0.25 kg
Shunt Weight: 0.7 kg
Technical Documentation: Aircraft electrical system documentation, instrument passport, calibration documentation

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