Local logic and alarms without a PLC: IF-THEN rules on WISE modules

Many monitoring tasks need a small amount of logic: switch on a fan when the temperature rises, send an alarm when a door stays open, stop a pump when the level is too low. A PLC can do this, but it needs programming software and someone who maintains the program. ICP DAS WISE modules run IF-THEN rules that are configured in a web browser instead. This article explains how the rule engine works, shows a worked example, covers data logging and notifications, and describes where the limits are compared with a PLC.

How WISE IF-THEN rules work

Every WISE module has a built-in web interface. You open it in a browser, define the rules on web pages and save them to the module, where they are executed. No programming tool or extra software is needed. Each rule has three parts:

• IF: a condition, for example an analog value above a limit, a digital input state or an expired timer.
• THEN: what happens when the condition is true, for example switching an output, starting a timer, changing an internal register or sending an email.
• ELSE: an optional action when the condition is false.

Besides the I/O channels, the rules can use timers, internal registers and recipe operations, and schedules let rules act at set times. The edge controllers also provide mathematical operations. Modules can send CGI commands to IP cameras and other network devices, so a rule can trigger an action in another device.

Worked example: an unmanned technical room

A WISE-7526M monitors a small technical room. It has 6 analog inputs, 2 digital inputs, 2 digital outputs and 2 analog outputs, and it is powered over PoE. The signals are wired as follows: AI0 room temperature (4 to 20 mA transmitter), AI1 humidity, DI0 door contact, DI1 UPS alarm contact, DO0 extra cooling fan, DO1 warning beacon. Limits are shown in °C for readability; enter them as the input values that match the transmitter range.

Rules 1 and 2 use two thresholds, so the fan does not switch on and off around a single value. Rules 5 to 8 use timers as delays, so a door opened briefly for maintenance or a short UPS event does not cause an email. Test how the module behaves while a condition stays true, so a persistent alarm does not flood the mailbox. Meanwhile the module publishes its values over MQTT to a central broker for a dashboard.

One practical point: WISE-7100 and WISE-75xxM I/O modules send email without SSL. Many mail services only accept encrypted connections, so plan for a local mail relay, or use a WISE edge controller, which supports SSL email.

Data logging and notifications

The WISE I/O modules (WISE-7100 and WISE-75xxM) do not list a data logger. They make their values available over Modbus TCP, and the WISE-75xxM models also over MQTT, so a SCADA system or broker records the history.

WISE-5800 adds a data logger with microSD card. It records I/O values by event or at regular intervals and sends the files by email or FTP. It reads I-7000 remote I/O modules or Modbus RTU devices.

The edge controllers WISE-5231M, WISE-2241M and WISE-2841M support an unlimited number of rules, timers, schedules and data logger sets, with a built-in 32 GB microSD card. They read XV-board I/O, RS-485 modules and Modbus TCP devices, and push data actively by MQTT publish, Modbus TCP or SNMP trap. Notifications include SSL email, SMS on the 4G models and messaging apps such as Telegram on WISE-2841M. All WISE edge controllers work with IoTstar for central monitoring and remote maintenance.

Which WISE model fits

Examples: WISE-7144 (8 DI, 8 DO), WISE-7105 (8 thermistor inputs, 4 DO), WISE-7526M and WISE-7555M (MQTT). WISE-5231M-4GE and WISE-2841M-4GE have a built-in 4G modem for EMEA frequency bands.

Limits compared with a PLC

• Type of logic. Rules suit thresholds, interlocks, delays and time-based switching. Sequences with many steps, state machines and closed-loop control are easier to build and maintain in IEC 61131-3.
• Speed. The data sheets do not state a rule execution time, and the analog inputs are not made for fast signals: WISE-7526M samples at 10 samples per second in total. Use a PLC or PAC for fast signals and time-critical control.
• Capacity. The I/O modules have fixed limits of 36 or 72 rules. Larger applications need an edge controller or a PAC.
• Safety. Rules are not a safety function. Emergency stops and safety interlocks belong in hardwired or certified safety equipment.
• Documentation. Rules are easy to change in a browser, which also makes them easy to change without a record. Keep a written description of the rule set.

When the limits are reached, ICP DAS Win-GRAF PACs run IEC 61131-3 programs, and the UA series communication servers include a PID function. For networks with stricter security requirements, ETS-7200 Ethernet I/O such as ETS-7255 also offers IF-THEN-ELSE logic together with HTTPS and MQTT with optional TLS.

Send us a list of your signals and the logic you need, and our technical sales team will suggest a suitable WISE model or an alternative.