How to setup a Cortex320 Versatile Metering Input as a Digital Input

The Cortex320 has 4 dedicated opto-isolated Status Inputs and 12 Versatile Metering Inputs. Should you run out of Status Inputs, any of the 12 Versatile Metering Inputs can be set to behave like a Status Input.

There are generally two ways of monitoring dual-state logic levels with a Status Input:

  1. from a two-level Hi/Lo voltage with a ground return (known as “wet” circuit),
  2. from a contact closure/opening (known as “dry” circuit).

The Cortex320 Versatile Inputs can accommodate both ways, and we will go through the setup steps for both of them.

Monitoring a two-level voltage-based logic signal

Configuring a Cortex Versatile Input to discriminate between two different voltage levels (Lo/Hi) is easy, and only requires connecting to the unit and going to the configuration menu of the desired Metering Input. As an example, let’s consider a sensor that provides an output voltage that switches between 0 Volts for a normal condition (Lo), and 5 Volts for an active/alarm condition (Hi).

Knowing what the Lo and Hi voltage values are, we simply take the halfway (middle) voltage value which will serve as a pivot point to determine when the measured voltage is Lo (below the pivot point) or Hi (above the pivot point). For this example, the pivot point value is 2.5 Volts. It could also be anywhere between 1 Volt and 4 Volts, as long as it’s not too close from either 0 Volt or 5 Volts. This principle could also apply for a situation where the readings would come from an SNMP GET command.

To configure a Metering Input to behave as described above, go to the configuration screen of the desired Metering Input and set the LEVEL 1 High Limit to 2.5 (or any other value of your choice). If you experience triggering issues, you may want to try a different value, or set a small Hysteresis value, available in the same configuration screen.

By default, the Cortex320 Workspace Meters have a scaling set between 0 and 100, but for a situation like the one we are examining here, changing the scale to 0 – 5 gives a better view, a bit like zooming-in the area of interest. With this setup, the 0 – 2.5 Volts green zone represents the Lo/Normal level, and the 2.5 – 5 Volts cyan zone represents the Hi/Active level. If you would like to change the Meter scale or appearance, please see the Introduction to Workspace Edition, Creation and Saving and Introduction to Cortex Meter Edition and Creation articles.

If you instead need the logic behavior to be the opposite of the one described above, which is when the voltage at the Metering Input’s terminals is below 2.5 Volt, it is considered as a logic Hi/Active level, and when the voltage at the Metering Input’s terminals is above 2.5 Volts, it is considered as a logic Lo/Normal level, set the LEVEL 2 Low Limit to 2.5 (or any other value of your choice). If you experience triggering issues, you may want to try a different value, or set a small Hysteresis value, available in the same configuration screen.

With this setup, as shown below, the 0 – 2.5 Volts cyan zone represents the Hi/Active level, and the 2.5 – 5 Volts green zone represents the Lo/Normal level.

Monitoring a two-state contact-based logic signal

By default, the Cortex320 Versatile Metering Inputs behave like any typical Metering Input, which is to read and display variable analog voltage signals. In order to be able to monitor a non-powered (or dry contact) logic signal, a small setting to the Versatile Metering’s input circuit is required, which is to provide some power to it. This is achieved through the use of a pull-up resistor (as often seen with typical digital inputs), and it can be set/unset with a small DIP switch located inside the Cortex320.

To set such a pull-up on a Cortex Versatile Metering Input, begin by removing power from the unit, then discharge any static electricity that you or the unit may have accumulated. Remove the top cover and locate the two DIP switches highlighted in red in the image below. The left DIP switch (S3) sets the pull-up resistors for Versatile Metering Inputs 1 to 8, and the right DIP switch (S1) sets the pull-up resistors for Versatile Metering Inputs 9 to 12. When a specific switch is in the IN position, the corresponding Versatile Metering Input becomes usable as Status Input (and can no longer be used as a Metering Input, unless its DIP switch is set back to the OUT position).

The image below is a close up view of the two DIP switches area.

Also, it is required that the VOLTAGE RANGE jumper of the matching Versatile Metering Input be set to the 5V position, (which is the factory-default position). As highlighted below, these jumpers are located in the middle of the board, slightly to the right. A close-up view is given further below.

Close up view of the first few VOLTAGE RANGE jumpers, with the 5 Volts positions highlighted in red (factory-default position).

This concludes the internal hardware setup. The cover can be reinstalled. We will now proceed to configure the software Versatile Metering Input configuration.

A Versatile Metering Input that is set with a pull-up resistor automatically displays a voltage value around 2 Volts (Hi) when an open circuit is applied to its input terminals, and displays a voltage value around 0 Volt (Lo) when a closed (or short) circuit is applied to its input terminals.

Knowing what the Lo and Hi voltage values are, we now need to set a mid-point voltage value which will serve as a pivot point to determine when the measured voltage is Lo (below the pivot point) or Hi (above the pivot point). For this example, the pivot point value is the exact middle range voltage, which is 1 Volt.

To configure a Versatile Metering Input to behave as described above, go to the configuration screen of the desired Metering Input and set the LEVEL 1 High Limit to 1. If you experience triggering issues, you may want to try a different value, or set a small Hysteresis value, available in the configuration screen.

By default, the Cortex320 Workspace Meters have a scaling set between 0 and 100, but for a situation like the one we are examining here, changing the scale to 0 – 2 gives a better view, a bit like zooming-in the area of interest. With this setup, the 0 – 1 Volt green zone represents the Lo/Normal level, and the 1 – 2 Volts cyan zone represents the Hi/Active level. If you would like to change the Meter scale or appearance, please see the Introduction to Workspace Edition, Creation and Saving and Introduction to Cortex Meter Edition and Creation articles.

If you instead need the logic behavior to be the opposite of the one described above, which is when the voltage at the Metering Input’s terminals is below 1 Volt, it is considered as a logic Hi/Active level, and when the voltage at the Metering Input’s terminals is above 1 Volt, it is considered as a logic Lo/Normal level, set the LEVEL 2 Low Limit to 1 (or any other value of your choice). If you experience triggering issues, you may want to try a different value, or set a small Hysteresis value (available in the configuration screen).

With this setup, as shown below, the 0 – 1 Volt cyan zone represents the Hi/Active level, and the 1 – 2 Volts green zone represents the Lo/Normal level.

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