Articles & Technical Notes

How do I set the PCO-7810’s pulse frequency (pulse repetition rate)?

A trigger source sets the pulse frequency. Either the PCO-7810’s internal trigger source, or an external source, can be used. (The width of the pulse is fixed and varies with the model.)

Due to power dissipation limits, each model has a maximum specified pulse frequency. Specifically:

  • The PCO-7810-40-4 can output pulses up to 40 A at rates up to 200 kHz, but it requires forced air cooling above 100 kHz.
  • The PCO-7810-50-12 can output pulses up to 50 A at rates up to 67 kHz, but it requires forced air cooling above 25 kHz.
  • The PCO-7810-90-8 can output pulses up to 90 A at rates up to 25 kHz, but it requires forced air cooling above 10 kHz.

External Trigger

To use an external trigger source, set rotary switch SW2 to position 1 and feed the trigger pulses into pin 1 of DE-9 connector P1.

Internal Trigger

The internal trigger source consists of a variable-frequency RC oscillator driving a frequency divider IC. There are three user frequency adjustments: Rotary switch SW2 chooses the frequency divider ratio; two-pole dipswitch SW1 lowers the frequency of the oscillator by adding capacitance; and pot R11 does the fine adjustment. This arrangement provides a very wide range of pulse frequencies.

You can use an oscilloscope to examine the trigger pulses at test point E2, located near SW2.

Choose a coarse frequency range by setting SW2 to a position from 2 to 9 (see chart). If needed, set one or both poles of SW1 to the ON position to reduce the frequency. Set the exact frequency with R11.

The following table summarizes the functions of SW2.

Position

Frequency Range

1

External Trigger

2

15 Hz to 60 Hz

3

50 Hz to 240 Hz

4

200 Hz to 985 Hz

5

775 Hz to 3.8 kHz

6

3.5 kHz to 15 kHz

7

13 kHz to 63 kHz

8

25 kHz to 126 kHz

9

50 kHz to 249 kHz

0

Internal source OFF


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