Resources / Case Studies / Multi-Chamber PID Pressure Control

Multi-Chamber PID Pressure Control

In this use case, you'll learn how to control the pressure of a reaction chamber using off-the-shelf ICs.

Application Challenge

High accuracy pressure control is a common requirement for many physical processes in biochemical, semiconductor and process control industries. OEM machine designers need an off-the-shelf and cost-effective solution for single as well as multiple chambers that provides accurate PID (Proportional, Integral, Derivative) control and flexible pressure control profiles.

Application Considerations

Feature/Function

Unit/Description

Pressure control range

800 - 25,000 millibar

Pressure control accuracy

10 millibar

Pressure control resolution

2.5 millibar

# of chambers

3


Control Solution

Figure 1 below shows the major elements of the proposed solution: a linear pressure sensor that outputs an analog voltage, signal conditioning and A/D circuitry, a Magellan PID controller IC, output signal conditioning and a voltage-controlled flow valve. A host PC or microprocessor communicates to the PID controller IC and provides overall sequencing and control of all three reactions chambers.

We will use a Magellan positioning IC to provide the pressure control profile generation and PID pressure control. This chip is more commonly used to control motors, but will serve just as well to control pressure.

Pressure Valve Application System Diagram
Figure 1: Pressure Valve Application System Diagram

 

The Magellan receives its parallel-word input by the analog voltage after it is converted to a digital signal. The Magellan's SPI output mode is used to create a command voltage to the valve using an SPI-input drive chip. There are several different types of valve control signals, such as 4-20ma signal and the +/- 10v dc signal, which will dictate the SPI drive chip to be used. This application will use a 4-20ma signal.

Components

Specification

Description

Analog-digital IC

AD7572

Input feedback signal A/D converter

Digital-analog IC

AD1866 (SPI)

The AD1866 uses the SPI input and output voltage signals

Controller

PMD Corp's Magellan MC58000 IC

Off the shelf Motion Control IC

The table above shows the block diagram for the pressure profiling and PID controller. The Magellan's flexible architecture can be used to set a desired pressure, create pressure profiles with linear or parabolic ramps and set breakpoint conditions such as 'automatically change to a new target profile after a specified pressure setpoint is reached'.

 

PID Control Algorithm
Figure 3: PID Control Algorithm

 

The PID sample/output rate should be set to match the system response. For typical pressure controllers, this means setting the PID loop sample time to between 10 mSec and 1 sec.

Going Further

The Magellan IC can also be used to control temperature. In fact, it is common to control both pressure and temperature in a single reaction chamber. This would take up two 'axes' of the Magellan control IC. The principle of control is the same; the input sensor provides the current temperature and the output from the PID drives a heater/cooler.

Motion Control Chips and CardsThe Magellan® Family of Motion Control ICs provides high performance chip-based motion control for multiple motor types. Magellan motion control ICs are available in 1, 2, 3, and 4-axis versions. They are designed for demanding and precise applications such as this pressure valve application and other automation and instrumentation challenges.

Want to learn more? Contact our customer support team today for more information, including details on Developer Kits and application support. We would like to assist you in improving your motion system.

 

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