37
Requirements for pulse ammeter
1. Three-phase four-line active pulse ammeter
A. The ammeter shall be suitable for metering three-phase AC active electric energy at a rated
frequency of 50 Hz.
B. The number of pulses outputted by the ammeter for one kWh of electricity shall be constant.
C. The amplitude of the pulse signal shall be 5 Vdc and the width of every pulse shall not be less
than 80 ms.
D. The pulse signal from the ammeter shall be passive, that is, an external pulse signal is
required for the ammeter to generate the required control power supply.
2.Both mechanical and electronic ammeters shall be used as long as they meet the above
requirements. According to the total power input of all the outdoor units, the parameters of
ammeter shall be defined such as rating current.
The wiring of ammeter includes 3 methods:
Direct connection;
Connection via current transformer;
Connection via current and voltage transformers (seldom used).
Direct connection method has low cost as there are no current and voltage transformers employed.
However, if the operation current is out of ammeter current range, the transformers are required.
3. The recommended ranges of ammeter for different horsepower of outdoor unit are shown
in the following table; if the range of ammeter is insufficient in direct connection method,
transformer method shall be used.
4. Example of ammeter used in China
For total 36 Horsepower outdoor units system:
If the ammeter capacity is 30(100)A, 200Pulse/kWh, pulse width
80+/-20ms, Direct Connection type is feasible.
If the ammeter capacity is 20(80)A, current transformers are
required.
Total horsepower of
outdoor units
Range of ammeter
10-60A
20-80A
30-100A
30-120A
≤20
≤30
≤40
≤48
Electric wiring and the application
