I am working on project to keep preset temperature inside chemical reactor by changing cooling water amount pumped through reactor. Because quite high precision is needed I was thinking about PT100 (class A or B 1/10) sensor as temperature pick-up. The first idea was to PWM cooling water DC pump but after reading I decided to go proportional solenoid valve instead.
After searching similar projects in internet following circuit came up - http://gillesenergies.webs.com/evalve.htm. As I understand from SSR used the solenoid switching frequency is not very high and simple/cheap NC (normally closed) 12VDC solenoid valve is used which is very temptating because of price difference.
Unfortunately I can not understand how this circuit works (555 and IC1D). Tried to simulate with different R17, R18 and C3 values on Tina TI but could not get oscillating waveforms like on diagrams.
Can someone lead to right track?
After searching similar projects in internet following circuit came up - http://gillesenergies.webs.com/evalve.htm. As I understand from SSR used the solenoid switching frequency is not very high and simple/cheap NC (normally closed) 12VDC solenoid valve is used which is very temptating because of price difference.
Unfortunately I can not understand how this circuit works (555 and IC1D). Tried to simulate with different R17, R18 and C3 values on Tina TI but could not get oscillating waveforms like on diagrams.
Can someone lead to right track?