Selecting the Signal(s) to Monitor For Automated Counts

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 below:

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 (and only 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.

Counting Total Cycles

This is almost always what you will be doing. When in doubt, assume you’ll be counting total cycles.

In the majority of cases, you will be looking for a signal that represents the “total” number of cycles. In other words, this signal should trigger once per cycle (regardless of whether the part ends up being “good” or “bad”). Most machines don’t know whether a part is “good” or “bad”, so usually the number of bad/scrap parts is determined after parts have left the machine. This information can be manually entered by an operator through the app so that final counts are accurate.

Counting Good and Bad / Scrap Cycles Automatically

For machines that DO automatically sort out good or bad parts, you can monitor the counts for any combination of two count types (total, good, or bad) and Amper will do the math to give you all three count types automatically. For “good” or “bad” count types, the signal should ONLY trigger for cycles that correspond to a “good” or “bad” part cycle, respectively.

Combining Multiple Inputs of the Same Count Type

In some cases, no single 24V control signal covers every scenario where a cycle occurs. If this is the case, you can connect multiple different control signals for the same type of cycle (total, good, bad, etc). Once connected and configured, Amper will sum all relevant counts for each type of cycle (for example, both sources of "total" cycle counts will be added together).

For example, your machine may have two different physical locations where parts exit the machine depending on size, each with its own signal indicating a cycle has occurred. In this case, you would connect each signal to its own input on the digital aggregator, following the appropriate instructions in the following article for each.

NOTE: If these different count sources operate off of a different electrical power supply from one another, you may need to use multiple digital aggregators to ensure they remain isolated from one another.

Common Sources of Signals To Consider Monitoring

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. See the following article for additional information on adding a load when required.

Next Steps

Next, you will need to connect your Digital Aggregator to power and the appropriate signal(s) in your machine.