Druck DPI 530, User Manual

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20 DPI 530 User Manual
K162 Issue No. 2
3.1.3 Functional Description (Figure 3-1)
The instrument's controller uses pneumatic valves to control the flow
(pressure) of the gas from a source pressure. The valves are energised
by a pulse width modulated signal. A transducer mounted on the manifold
measures the pressure and produces a feedback signal proportional to the
outlet pressure. The error amplifier compares this signal with the set-point
signal to produce a bipolar error signal proportional to the difference. The
control conditioner buffers the error signal to drive the PWM which, in turn,
drives the pneumatic valves to change the output pressure towards the
set-point.
As the outlet pressure changes towards the set-point, the transducer
output changes and the error signal decreases until the system balances
at the set-point. When the system balances a ready signal illuminates the
`Ready' LED. The ready signal also supplies an opto-isolated open
collector NPN transistor that can be used to supply an external solenoid or
relay.