Process Control Systems (PCS) - Supply Chain Management

PCS can gather and submit data during manufacturing

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Introduction

Process control systems (PCS), sometimes called industrial control systems (ICS), are pieces of equipment along the production line that can be supervisory control and data acquisition (SCADA), programmable logic controllers (PLC), or distributed control systems (DCS), that can gather and transmit data that is obtained during the manufacturing process.

The PCS can be a relatively simple item that can have a sensor, often called a primary transducer, that receives an input, a controller that processes the input, and a receiver that processes an output.

More complicated PCS devices can be robotic in nature and perform many tasks. The PCS devices can communicate with a company’s enterprise resource planning ( ERP) application through middleware software called a manufacturing execution system (MES).

Sensors

There are a great number of measurements that can be taken on a production line. The sensor can take many measurements including pressure, flow rate, density, acidity, velocity, speed, stress, temperature, and weight.

In addition, sensors can detect if an operation has occurred, such as the fill of a bottle, the correct pressure has been achieved, or a temperature has been reached.

There are many sensors that can be found on the production line, that fall under a number of different areas, such as pressure sensors, flow meters, force sensors, and temperature sensors.

Pressure Sensors

A pressure sensor can be triggered mechanically as an item passes the sensor.

In its basic form, a pressure sensor shows the reading on a dial attached to the sensor but can also electronically transmit the reading to the MES application.

  • Piston Pressure Sensor - The pressure from the item on the production line can push on the piston which compresses a spring. The movement of the spring can indicate the pressure.
  • Diaphragm – The diaphragm is affected by small amounts of pressure and these are indicated on a dial.
  • Bourdon Tube – This is a hollow tube that is straightened when pressure is applied. It can be used for measuring pressure differences.

Flow Meters

A flow meter is an instrument used to measure linear, nonlinear, mass or volumetric flow rate of a liquid or a gas.

When selecting a flow meter for the production line, you need to know information about the fluid involved, the rate of movement, and how to record the flow.

  • Positive Displacement – These flow meters use a mechanical effect to measure flow. The speed of the rotation of the meter indicates the flow of the liquid.
  • Differential – The differential flow meter identifies the flow and converts that to a differential pressure which can be measured.
  • Inferential – The inferential flow meter measures the flow based upon an effect of the flow. This could be a simple rotor arm that is moved by the flow; the faster the rotor moves, the faster the flow.

Force Sensors

A force sensor is used to measure forces and torque exerted. These sensors usually contain strain gauges and can communicate information required for force measurements. Force sensors can be mechanical, hydraulic, or electrical strain gauges.

  • Mechanical – These are similar to the operation of a normal scale, where a spring is moved when force is applied. The deflection of a spring is directly proportional to the applied force so if the movement is shown on a scale.
  • Hydraulic – Often referred to as hydraulic load cells. The cell contains liquid, which becomes pressurized when a force is applied. The measurement is taken by a dial showing the pressure.
  • Strain Gauge – This is a metal cylinder which is compressed when a force is applied. The contraction in the cylinder can be measured causes increased resistance measured by an applied electrical current.

Temperature Sensor

A temperature sensor converts the temperature into another quantity such as mechanical movement for a dial or an electric voltage.

  • Thermocouple – Thomas Seebeck discovered that when any conductor is subjected to a thermal gradient, it will generate a voltage. Thermocouples are usually wires insulated from each other with plastic or glass fiber materials.
  • Liquid Expansion – These sensors are thermometers that can be filled with mercury or an evaporating fluid that are used in refrigerators. Temperature changes produce expansion or evaporation of the liquid so the sensor becomes pressurized. The change is shown on a simple pressure gauge.
  • Bimetallic – When two metals are rigidly joined together as a two-layer strip and heated, the difference in the expansion rate causes the strip to bend. For sensors on the production line the strip is twisted into a long thin coil inside a tube. One end is fixed at the bottom of the tube and the other turns and moves a pointer on a dial.

This PCS article has been updated by Gary Marion, Logistics and Supply Chain Expert.