Sharp JX-9400 Technické informace stáhnout pdf (Strana 122)

simultaneously the r.m.s. voltage, U, between phase and neutral point, the

r.m.s. current, I, running into each motor coil and the phase shift, ’, between

voltage and current. The power is calculated by:



j ¼1

cosð’

Þð5:54Þ

the sum being on all three phases.

In very small air handling units, the fan motor may be single phase, and



¼ UI cosð’Þð5:55Þ

To measur e the current an ampere-meter must be installed in the circuit. An

easy way is to use clamp-on ampere-meters. A measuring clamp is installed

around each wire leading to the motor. This clamp contains a transformer

that gives a current proportional to the current running through the closed

clamp. Care should be taken not to install the clamp around the two -wire or

four-wire cable. The measured current will be zero in this case, whatever the

power used by the motor.

In some air handling units, the fan is controlled by a variable frequency

controller (see Figure 5.15). Such devices are often equipped with a screen

Figure 5.15 Front panel of the variable frequency controller

Measurements and Measures Related to Energy Eﬃciency in Ventilation 101

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Sharp JX-9400 Technické informace Strana 122