Writing PLC control signals when conditions are met

SpeeDBee Synapse:v4.9.9Last updated:2026-09-15

Purpose

Write control signals or instruction values to a PLC when values collected from the PLC meet specified conditions.

Project files

These are the project files used in this example. A standard version and a version with the PLC Collector configured in simulation mode are available.

• PlcWritingOnCondition.sspj
• PlcWritingOnCondition_Sim.sspj (simulation mode)

Note: Import requires SpeeDBee Synapse version 4.9.9 or later.

What you will learn

• How to use data collected from a PLC for condition evaluation
• How to use the Compute Collector to evaluate a condition based on multiple collected values
• How to use the Event data component to output data for writing only when a condition is met
• How to use the PLC Writing component to write a value to a specified PLC address

Requirements

Collect equipment status and measurement values from a PLC, then write a control signal to the PLC when the condition is met.

For this example, assume the following data is collected from the PLC.

Data name	Example address	Data type	Description
operation_mode	D0100	WORD	Operating mode. 1 indicates automatic operation.
temperature_c	D0101	WORD	Temperature (degrees C)
pressure_kpa	D0102	WORD	Pressure (kPa)

When the condition is met, write a control signal to W100.00 in the PLC.

Example write address	Data type	Value to write	Condition
W100.00	BIT	1	operation_mode = 1 and temperature_c >= 80 and pressure_kpa >= 500

About the write address

Specify an address that is approved for control use on the PLC side. Writing to an address used by existing control logic or manual operation may cause unintended behavior. Check the PLC ladder program and control specifications before configuring the address.

About the write condition

The PLC Writing component writes input data to the PLC. When a condition must be evaluated using multiple values as in this example, the Event data component alone cannot perform the evaluation. Add a Compute Collector so that it outputs 1 when all collected values meet the condition and 0 otherwise. Configure the Event data component to output result to the subsequent PLC Writing component only when this result is 1.

Components used

• PLC Collector (collects data used for condition evaluation)
• Compute Collector (evaluates the write condition based on multiple collected values and outputs 1 or 0)
• Event data (outputs data to the subsequent component only when the Compute Collector output is 1)
• PLC Writing (writes to the PLC when triggered by data from Event data)

Workflow

1. Collect operation_mode, temperature_c, and pressure_kpa with the PLC Collector.
2. Use the Compute Collector to output result = 1 when all collected values meet the write condition, and result = 0 otherwise.
3. Use the Event data component to output a value only when result = 1.
4. When result is received from Event data, use the PLC Writing component to write 1 to W100.00.

The data flow is shown below.

Setup

1. Configure the PLC Collector. Specify the PLC connection target, collection interval, and addresses to collect so the data required for condition evaluation can be collected.

   

   Data name	Example address	Data type
   operation_mode	D0100	WORD
   temperature_c	D0101	WORD
   pressure_kpa	D0102	WORD

2. Add a Compute Collector and connect it to the PLC Collector. When registering a new Compute Collector, a dialog appears to select the component to connect to the input port. Select the PLC Collector configured in step 1 and click CONNECT.
   Note: The PLC Collector must be running before it can be selected. Start it in advance using the ▶ button if necessary.

   

3. Configure the input data and formula for the Compute Collector. First, assign the data received from the PLC Collector to $A, $B, and $C in the input data settings.

   

   Variable	Input data
   $A	operation_mode
   $B	temperature_c
   $C	pressure_kpa

   Set the following formula and set the output data name to result. The component outputs 1 when $A, $B, and $C all meet the condition; otherwise, it outputs 0.

   

   Output data name	Formula
   result	IF($A = 1 AND $B >= 80 AND $C >= 500, 1, 0)

4. Add an Event data component and connect it to the Compute Collector. When registering a new Event data component, a dialog appears to select the component to connect to the input port. Select the Compute Collector configured in the previous step and click CONNECT.
   Note: The Compute Collector must be running before it can be selected. Start it in advance using the ▶ button if necessary.

   

5. Configure the Event data component to output result to the subsequent component when the result received from the Compute Collector is 1. Select raise as the condition type and specify $VALUE = 1 as the condition expression ($VALUE = result). This outputs data only when result changes from 0 to 1.

   

   Input data	Condition type	Condition expression
   CalculateWriteCondition:result	raise	$VALUE = 1

   About the condition type

   When true is selected as the condition type, data continues to be output while the condition expression is met. To write to the PLC only when the condition changes to true, use raise.

   Do not pass data to the PLC Writing component while the condition is not met. This causes PLC writing to be performed only when the condition is met.

6. Add a PLC Writing component and connect it to the Event data component. When registering a new PLC Writing component, a dialog appears to select the component to connect to the input port. Select the Event data component configured in the previous step and click CONNECT.
   Note: The Event data component must be running before it can be selected. Start it in advance using the ▶ button if necessary.

   

7. Select the PLC to write to as the connection target. Assign result, which is output from the Event data component, as the input data. Configure the component to write the fixed value 1 to W100.00 when result is received.

   

   Trigger data	Example write address	Data type	Fixed value to write
   DetectWriteCondition:ed1-CalculateWriteCondition-result	W100.00	BIT	1

8. Configure the delay time in the input port settings of the PLC Writing component. When components such as the Compute Collector and Event data are used in the flow, a delay occurs before data reaches the PLC Writing component. Set a delay time to shift the input data search range by that delay. In this example, set it to 6000ms. For details about the delay time, see Delay time.

   

9. Save the settings and start each component.

   

Operation check

Change PLC values and confirm that 1 is written to W100.00 when the condition is met.

Check the output data from the PLC Collector and Event data component. Confirm that Event data outputs result(1) only when the condition is met. In the following example, result(1) is output at 10:53:57.

Next, check the PLC Writing component log. Confirm that the log shows writing was performed at 10:54:04.594, approximately 7 sec after result(1) was output at 10:53:57. This approximately 7 sec interval includes the configured 6000ms delay time and other processing time.

Notes

Delay time

If the actual delay before the data arrives is longer than the configured delay time, subsequent components may not be able to retrieve the input data. This occurs because the output data is delayed and no longer falls within the input data search range of the subsequent components. If the input data cannot be retrieved, subsequent components do not perform processing such as output and writing. The delay time shifts this search range. Set it based on the delay before the data arrives.

For an Event data component, use the DEBUG log as a guide for the delay time.

In this example, the approximately 4.1 sec difference between the insert time and the timestamp assigned to the data is the delay. In this example, allowing for this time and setting the delay time to approximately 6000ms enables the input data to be detected.

Insert time	Assigned timestamp	Diff
2026-09-15T09:47:27.183	1789433243063622411 (2026-09-15T09:47:23.064)	4.119s
2026-09-15T09:47:42.192	1789433258063622411 (2026-09-15T09:47:38.064)	4.128s
2026-09-15T09:47:57.200	1789433273063622411 (2026-09-15T09:47:53.064)	4.136s