KNX hysteresis in Link’nX: command an output with two thresholds

The Hysteresis function in Link’nX monitors a numeric KNX measurement, for example a temperature, and sends a value to a target group address when the measurement reaches a low or a high threshold. Between the two thresholds, the deadband causes no sending.

Intended for installers and administrators who have the KNX measurement and the parameters of the target command. The procedure covers a numeric source, with its corresponding DPT. For a binary source, contact support to establish the procedure suited to your need.

Open the hysteresis form

In Functions, click Add, fill in Function name, then choose Hysteresis in Function type. For an existing function, open its Edit pencil.

Fill in the source, the target and the thresholds

1. In Hysteresis settings, Source block, fill in KNX group address, then the DPT of the measurement in the small data type field below the address, which shows the example 9.001.
2. In the Target block, fill in KNX group address, then the DPT of the command in the small field below the address, which shows the example 1.001. The source and the target can have different DPTs: choose each one according to its actual use.
3. Fill in Low threshold and High threshold in the unit of the source measurement. The low threshold must be strictly lower than the high threshold: two equal thresholds are rejected.
4. Fill in Low threshold output value and High threshold output value according to the DPT and the target command. For a target of the DPT 1 family, choose 0 (false) or 1 (true) in each list; for a numeric target, enter the appropriate values. Reread these two values after any change of the target DPT. The output values guide also covers the text case.

Address format: three levels separated by slashes without spaces, the first from 0 to 31, the second from 0 to 7, the third from 0 to 255. DPT format: a main number from 1 to 999, a dot, then three or four digits. 1/1/1 and 9.001 are fictitious examples to replace with the parameters of your installation.

Understand how the thresholds trigger

On a numeric source, the function behaves as follows:

Value received	Zone	Effect
Lower than or equal to the Low threshold	Low zone	Requests the low threshold output value when entering the zone
Between the two thresholds	Deadband	No sending
Greater than or equal to the High threshold	High zone	Requests the high threshold output value when entering the zone

Successive values within the same low or high zone do not repeat the command. A return to the deadband, then to a threshold zone, allows a new sending. The first measurement received after commissioning can therefore request a command if it is already in a threshold zone.

KNX writes and responses carrying the measurement can be taken into account; a simple read request, without a value, does not count as a measurement.

Fictitious example: with a low threshold of 18 and a high threshold of 22, a measurement of 18 enters the low zone, 20 stays in the deadband and 22 enters the high zone. The output values are chosen for the equipment: this example does not set the heating or cooling commands suited to your installation.

Test the principle in the preview

To understand the principle without commanding the installation, use How it works in the preview:

• drag the round marker of the gauge: the zones light up when they are crossed;
• with the keyboard, select the marker, then move it with the up and down arrows;
• click Play demo to animate a simulation, and again to stop it while it is running.

These preview controls do not change the thresholds entered and send no KNX command.

Save the function

1. Check the Runtime interpretation, in particular the two thresholds, the values sent and the Destination:.
2. Check the Enabled or Disabled state.
3. Click Save or Update, then follow the confirmations described in the functions guide.

Check the result

In the list, the function card shows Source KNX, Target KNX, Low threshold and High threshold with the values to send. The preview remains a simulation: to see the real effect, watch the target equipment when the measurement enters a threshold zone.

Troubleshooting

• Low threshold must be lower than high threshold: correct the order of the two values.
• Invalid KNX group address or Invalid DPT format: check the format, then the parameter intended for the equipment.
• Binary source, unknown DPT or no result after the checks in the function troubleshooting: contact support@can-nx.com with the function, the context and the result you want.