What are the advantages and disadvantages of using analog vs digital I/O devices?

with some sensor applications, a High Speed Counter (HSC) discrete input can be used with a sensor that outputs pulse signals that vary in frequency (or pulse rate) in relation to the analog media being measured. Typically found in fluid measurement. Analog input modules are common place in the PLC world, as mentioned, they are typically more costly. Analog noise can be mitigated with good engineering practices in most applications. Using 4-20mA sensors is a good method. Isolated grounding for your analog signal wiring in the control cabinet. Also, using shielded twisted pair wiring and only terminating the shield on one end is a must for good wiring practices. Keeping your low voltage signal DC wiring away from AC wiring is also essential.

What can I add? With the increasingly cost effective remote I/O it makes a whole lot of sense to use an I/O module connected via fiber back to the PLC/DCS. And with the advancements in IoT devices which use encrypted private warless networks, the response time is significantly lower than what current DCS can offer. This, of course, hasn't been adopted by many industries yet, but it offers huge advantages. The disadvantages are: you are relying on a backbone line for a number of instruments in case of components failure, or human factor. These can both be mitigated by using redundant methods of communication either via a Fiber ring or Wireless. Properly specified wireless transmitter will operate for days prior to battery depletion.

Agreed, even a $5 arduino from Amazon will handle 16 separate discrete signals be they outputs or inputs with interrupts and not miss a beat. As already mentioned in the Analog I/O section, these can be combined to make a mesh private network with data encryption that is as hard to crack as any other RSA 4096 bit encryption out there.

Are you using scheduled tasks to evaluate time sensitive signals? If you look at digital conversion times in high speed IO and the fastest AD converters, the latency is sometimes two or three orders of magnitude different. Especially with chassis mounted IO adjacent the processor or EtherCAT, and optionally an interrupt process, there’s absolutely no way you have an analog signal that has lower latency than a digital one.

The choice between analog and digital I/O devices is application-specific. Influencing factors include scalability, where digital devices excel due to cost-effectiveness and ease of expansion. However, analog devices provide higher precision, crucial in some applications. Digital systems simplify maintenance and troubleshooting due to their binary nature, while analog devices, with variable signals, can be more challenging. In electrically noisy environments, digital I/O devices are preferred. Certain industries with strict regulations, like medical, may favor analog devices for precise measurements. Often, combining analog and digital devices yields optimal performance and flexibility.

Choosing between analog and digital I/O devices depends on data type and application needs. Analog devices excel in precise, continuous data handling (like temperature or pressure), ideal for industries requiring accuracy. Digital devices manage discrete signals (on-off), suitable for simpler operations and cost-effective solutions in various electronic systems. Consider nature, precision, cost, and compatibility when deciding.

Another method is using sensors that communicate with the PLC via Ethernet. Again, routing of the ethernet cord is important. We had a control cabinet built by a professional shop and all the ethernet cords for 40 VFDs in the cabinet were run in the same wireway as the 480VAC 3 phase power coming out of the VFDs. This created all kinds of random communication errors between the VFDs and the PLC.

Analog I/O s are the robust and very easy to troubleshoot and communicate...Digital I/O are best for ESD PLC or Opearting a remote unit with accuracy......

An advantage of analog devices is their ability to provide continuous range of values, allowing for more precise measurements or outputs. On the downside, since analog signals are susceptible to noise interference, there may be a loss in accuracy and reliability. Digital devices can offer better immunity to noise due to their binary nature. This makes them more reliable in environments with electromagnetic disturbances. Additionally, digital signals can be easily processed and manipulated by microprocessors or computers. However, when it comes to capturing fine details or subtleties in signals or information, digital devices might struggle as they operate on discrete levels rather than continuous measurements like analog ones do.

I’m going to again question what hardware you’re using. I can think of several platforms where you could sample your shot at less than 1ms on a PLC and derive arrays of data for as long as you’re willing to pay for memory for. And both would support writing that burst to a disk or network location, as well. Snarky comments aside, labview has its limitations when you have an actual process vs data collection. And frankly the learning curve sucks. Since you are really interested in PLCs with high sampling rates and data collection ability, I’d suggest looking at what Beckhoff is capable of. You can sample over 10,000 IO modules at less than 1ms with TwinCAT. You can build trends with 1-10ms update rates with the lowest end processor.

When selecting between analog and digital I/O devices, considerations extend beyond the nature of data and precision requirements. Evaluating factors such as cost, ease of implementation, scalability, and interoperability, especially when integrating products from different vendors, is crucial. For digital devices, adherence to standard communication protocols like Modbus or Profibus is essential, alongside comprehensive testing for compatibility. Analog devices, while simpler in signaling, require attention to calibration standards when integrating components from different vendors.

Also consider: Probably the most important 'detail' we missed is the process connection and installation detail. All the processing power in the world isn't going to help when you have a heavy crude line connected to a Pressure Transmitter via 1/2" tubing with no heat trace in sight... Always pay close attention to how, where, and any to install an instrument to provide accurate readings.