They denote the actual frequency difference corresponding to the inverse of time taken for one rotation of the illuminated vector spot. When two alternators are paralleled, it is necessary that voltage magnitude, frequency and phase must be same.

• Ideal visualisation on circular diod bargraph
• One or two range of input voltage
• Range of input signal: 57...500 V
• Frequency range:  35 - 70 Hz
• External dimensions:
  • 96 x 96 x 111.5mm (SA19 type)
  • 144 x 144 x 111.5mm (SA12 type)