Proportional Hydraulic Valve Control
Kirk Fraser
Posts: 364
How can I get proportional control so one valve coil is off and the other remains at the requested position (voltage) until told to change to a new position?
This is a continuation of thread "PWM to drive IRL530?" http://forums.parallax.com/showthread.php?127187-PWM-to-drive-IRL530 where the PWM command was explored with suggested use of MIC4420 to amplify the Stamp signal to drive the IRL530. I tried it and the amplification works but the PWM signal doesn't appear to produce a stable proportional output anywhere along the circuit. So I returned to the Shiftout command to send serial 12 bit data to a D/A chip TLV5618 and that output also didn't appear to work in producing a two channel proportional output directly, after op-amp LM530, or after the IRL530. Should I be using the MIC4420 before and/or after the D/A? What I typically get is one voltage that doesn't change on command, sometimes the same from both channels.
My program and a couple of circuits appear in this post:
http://forums.parallax.com/showthread.php?127187-PWM-to-drive-IRL530&p=969328&viewfull=1#post969328
The 12 bit data should produce a very precise charge, but what am I missing? Thank you.
This is a continuation of thread "PWM to drive IRL530?" http://forums.parallax.com/showthread.php?127187-PWM-to-drive-IRL530 where the PWM command was explored with suggested use of MIC4420 to amplify the Stamp signal to drive the IRL530. I tried it and the amplification works but the PWM signal doesn't appear to produce a stable proportional output anywhere along the circuit. So I returned to the Shiftout command to send serial 12 bit data to a D/A chip TLV5618 and that output also didn't appear to work in producing a two channel proportional output directly, after op-amp LM530, or after the IRL530. Should I be using the MIC4420 before and/or after the D/A? What I typically get is one voltage that doesn't change on command, sometimes the same from both channels.
My program and a couple of circuits appear in this post:
http://forums.parallax.com/showthread.php?127187-PWM-to-drive-IRL530&p=969328&viewfull=1#post969328
The 12 bit data should produce a very precise charge, but what am I missing? Thank you.
Comments
With respect, you should attach the circuit and code you're working on now. The word pictures in the post are quite confusing as you talk about PWM, proportional and 12-bit D/A in the same breath.
As we wrapped up the previous thread, I'm pretty sure you should be able to drive the mosfet from the Stamp with the PWM command and get a useful function out of the valve. No amplifier, no d/a, just the mosfet and valve.
By the way, are you using the valve by itself or did you also get the manufacturer's proportional module? If using the proportional module, it needs a real analog voltage and that will change everything we've been discussing.
Cheers,
Here's the current schematic and program.
Stamp Pgm.txt
The program reads the 10K Pot as position of the hydraulic actuator. The goal is to make it operate in an S-curve which is start slow, go fast, then reverse slow, so there is no jerk at end of travel. This loop is intended to test my setup for 1000 hours.
I was unable to get a smooth operation on my Oscope with PWM before or after the IRL530 with or without the amplifier. However I should try it off scope with the valve coils since maybe they cause something better to happen.
There are two coils in the valve but no electronics. The 3-way operation is A 0-24V, B 0-24V where the coil activated determines direction, the coil voltage determines speed, and both coils at zero voltage means stop.
Thank you.
Kirk
I think you're trying to generate a smooth analog value when the valve expects (and actually needs) a PWM signal. Nothing in your hardware or program is generating the PWM.
No question, what you see with the valves will be different than on a meter or scope.
If it were me, I'd set up a test with the Stamp, the IRL530 transistor and the valve and the following program:
' {$STAMP BS2sx} 'change this depending on the Stamp being used.
' {$PBASIC 2.5}
main:
PWM 5,150,50 ' change the 150 to change valve voltage, the 50 can be lowered slightly if desired.
PAUSE 20 ' depending on the length of the rest of the program, remove this pause
GOTO main
Cheers,
Thank you very much! I smoked the posted circuit when I added the coils but your suggested circuit directly connecting Stamp pins to IRL530's using the PWM command works!! It's also cheaper, less complicated, and easier.
The Shiftout command is much faster than PWM so I'm still hoping for a faster and more precise solution. But until then, I'll work on the foundation you've provided.
Kirk
Glad you were able to move forward!
Don't quite see the connection to Shiftout for this application, other than generation of some string of highs and lows, but keep us informed of your progress.
The PWM parameters can be played with quite a bit for tweeking purposes.
Cheers,
Tom