Puff Valve Driving
The EHT Pulse Amplifier can drive four independent miniature high speed, high vacuum pulse valves at higher actuation speeds than is possible using the working voltage level of the valves. It works by quickly energizing the valve with 250 V (labeled 300 V on front panel) for a short time of < 500 µs before providing an even 18 V “keep alive” voltage that holds the valve open at low power.
The Pulse Amplifier can operate any combination of pulse valves independently but the maximum repetition rate is halved for each additional valve driven simultaneously, i.e. 20 Hz for one valve, 10 Hz for two, 5 Hz for three, and 2.5 Hz for four actuated valves. It is possible to drive the valves faster than the advertised maximum without harm to the valves or the unit, but the valve opening characteristic may change depending on available charge on internal energy storage capacitors.
The following figures were determined with a Parker 28 V 70 Ω pulse valve load.
- Charge Voltage: 0 – 250 V
- Output Voltage: 0 – 250 V
- Keep Alive Voltage: 18 Volts
- Max Repetition Frequency (HV disabled): 100 Hz
- Max Repetition Frequency (HV enabled): 20 Hz single valve
- Max Pulse Width: 1 sec
- Min Pulse Width†: 300 µs for full actuation
- HV Decay time (250 V to 18 V): 800 µs
† Min pulse width figure is gathered from Parker pulse valve datasheet. It is possible to partially open the valve with much smaller pulse time.