use of PWM

[woollster]

Hi I have created a schematic for a project that will enable me to operate the solenoids on a valve unit. I would now like to add a PWM to allow the use of a duty cycle but I am not sure how to do this, any guidance would be appreciated.

Many thanks

I have attached the draft schematic for information.

Regards
Woollster

 

[alec_t]

Why do you need PWM for establishing a duty cycle? Is this for a 'peak-and-hold' type of energisation such as is used for fuel injectors? Or do you simply want to energise the solenoids repeatedly at varying intervals?

 

[woollster]

My plan is to energise the solenoids repeatedly at varying intervals? I am not clear on the use of PWM's as you may have guessed.

Thank you for your response.

 

[alec_t]

I think the choice is between :-
(1) A pulse generator which provides fixed-width pulses of just sufficient duration to actuate a solenoid and keep it actuated for the desired time, with the interval between pulses being variable. That is fairly straightforward.
(2) If saving current/power is important then the more complicated 'peak-and-hold' type of energisation would be needed during the fixed-width pulse duration, again with the interval between pulses being variable.

 

[woollster]

Hi alec_t

Thanks for your speedy reply, much apreciated.

I feel that option 1 is the best option, I now need to try and include this into my schematic which may prove more difficuult to do.

(1) A pulse generator which provides fixed-width pulses of just sufficient duration to actuate a solenoid and keep it actuated for the desired time, with the interval between pulses being variable. That is fairly straightforward.

Regards
Woollster

 

[alec_t]

Ok. So now the questions :-
(a) what is the minimum time needed for a solenoid to pull in?
(b) what is the required 'hold-in' time of a solenoid?
(c) what is the required range of time interval between successive actuations of a given solenoid?
(d) will each solenoid have its own timer or are the solenoids to be actuated in a fixed sequence from a single timer?
(e) how much current does each solenoid need to switch on reliably?