Selecting the Signal(s) to Monitor For Automated Counts

This article is about using the Digital Aggregator to collect automated cycle counts. To use a Digital Aggregator for utilization data collection, see the article,

Types of Signals That Are Compatible

The digital inputs on the Digital Aggregator are primarily intended to to sense 24VDC signals. These are the types of signals commonly used as sensor or PLC outputs, and are the most common type of digital signal. The signal requirements are as follows:

  • Voltage Type: DC
  • Voltage Range: 12-48VDC (higher voltages supported, but confirm with Amper first)
  • Signal Behavior: Binary state (signal is either high or low)
  • Input Impedance: 600k+ ohm for signals 12-24V, 100k ohm for signals 24V+
  • Input Current Consumption: <40uA at 24V

The device's digital inputs will not source or sink power from a sensor or PLC output. They are intended to measure existing signals. This allows for the device to avoid loading the signal. This also makes the inputs compatible with any signal polarity (PNP or NPN). It also works with a dedicated sensor output as long as the proper dummy load is connected.

Finally, the input only requires one wire, connected to the existing signal output. The two terminals per input are INTERNALLY CONNECTED for passthrough or termination if required.

Signal Selection

The key criteria for selecting a good signal to use is that it must change states back and forth once per machine cycle. For example, a part presence signal that triggers “High” once while the part is in place and returns to “Low” when the cycle is complete and the part is removed.

Using Dedicated Sensors or Signals

Many machines have sensors for part presence that input to the PLC, or a “job/part complete” signal that is sent out from the PLC. For machines that automatically sort out good vs. bad parts, there is usually a sensor or PLC output that controls the flow of the bad parts. Dedicated sensors are generally the easiest to install on. In this case, either the signal can be identified and traced directly from the sensor to an interconnect, or the sensor wire can be located via the machine’s manual.

Using “Production Ongoing” Signals

Many machines have a light that indicates production is ongoing, cycling on and off between parts. While these lights are usually AC electricity signals, there is often a DC control signal that determines when it turns on.

Using In-Process Signals

Sometimes a dedicated sensor or PLC output for part complete is not available. In this case, a signal should be identified that is triggered once per production cycle. Some common examples could include:

  • Safety guard that moves into place during cutting of a part and back away between parts
  • Door lock
  • Cycle start switch
  • Part ejector
  • Part presence signal
  • Injection molding valve gate
  • Injection molding ejector pin control

These are just a small subset of possibilities. Every machine can be slightly different. What is important is to identify a machine process that happens once per cycle.

Using an External Sensor

If your machine does not have a suitable signal that can correspond to machine cycles, then installing an external sensor may be the best option. This would usually be a proximity switch, light curtain, or line beam sensor. If connecting a dedicated sensor directly to the Digital Aggregator, a dummy load will usually need to be added as the Digital Aggregator does not source or sink current at the input.

Next Steps

Next, you will need to connect your Digital Aggregator to power and the appropriate signal(s) in your machine. For more information, please see our article