When to use digital pressure switches and digital sensors
Figure 1: Example of a digital pressure switch
Mechanical pressure switches were state-of-the-art solutions for control in manufacturing processes for quite some time. Nowadays the control of such processes are increasingly digital instead of analog. In addition, these modern pressure sensors allow for data collection and continuous process pressure output.
First, let’s look at why electronic pressure switches became so popular while analog versions also can perform the switching task. Although pressure sensors could provide all the needed information, supplying a control system or PLC with analog signals from each control point together with creating a control from these signals can be quite costly. For simple control systems, only one or two logic steps are often required.
Connecting and implementing an analog pressure signal to an electronic control unit (for example a PLC) has higher costs than using a direct switch output. For the cost of having a single analog input many switch contact inputs can be implemented. This allows for more switch points to be controlled and monitored for the same cost.
Now let’s look at why electronic pressure switches are so popular. Digital pressure switches have a much higher flexibility and reliability than mechanical ones. Depending on the specific digital switch, they offer one or two output switch signals and an analog output, while only having one pressure port.
Digital pressure switches combine a digital pressure sensor, for continuous data collection, with one or two mechanical switches to control the process within limit values. Reducing the amount of measuring points and ports and thus reducing the amount of switch products needed has a cost-saving benefit for the user. In addition, digital pressure switches simplify process control making them a great substitute for mechanical ones in the following applications:
- Replacing mechanical pressure switches implemented in a process line to allow for more control over the switch operations. This allows for local programming and a local LED display showing the actual pressure to assist operators or troubleshooting.
- Processes with vibration and/or many switching cycles. Digital pressure switches show to be more reliable in maintaining the switching points. They are less susceptible to fatigue and mechanical wear of the mechanical switches.
- Applications that need individual switching operation programming. For example, programming a reset point that deactivates the signal once the pressure passes the set pressure for a certain amount of time.
- If more precise local indication is needed. Digital pressure switches allow the operator to see the pressure trend locally at the machine or system.
- System oscillation prevention. Digital pressure switches have adjustable hysteresis of the switch points, this allows for more control in short cycle switching.
- Most digital pressure switches have an IO link which can be used to reprogram switches over a signal cable. This increases the system’s flexibility and allows for easier (re)programming of the switches.
Analog pressure transmitters will provide core information, but they are expensive to interface if the amount of transmitters becomes large. Digital pressure transmitters are cost-effective if a large amount of monitoring points are needed and controlled.