Using Temperature Controllers and Micro PLCs to Speed Small-Scale Automation Projects

Heat. It’s important in many industrial processes like packaging sealing machines, plastic molding operations, solder reflow ovens, semiconductor processing, etc. Each process has specific needs for temperature levels and control precision.

Automation helps achieve maximum productivity and sustainability in Industry 4.0 operations. Small machines and heat processing are no exceptions. But not all circumstances call for large, comprehensive solutions. Many applications can experience enhanced performance with relatively simple dedicated temperature controllers and small programmable logic controllers (PLCs).

Machine designers can choose from a range of options for simple automation projects, including heater controllers for single- and three-phase power environments, heater controllers with a range of sophisticated control algorithms, and PLCs optimized for small to medium-sized automation environments. Some small machines work in relative isolation, while others can benefit from connectivity to the larger operation.

This article presents a review of power controllers and heater controller options, including hardware and software considerations. It closes with a glance at system integration issues related to sensor technologies for measuring temperature and PLCs optimized for small to medium-sized machines and presents exemplary products from Omron.

From curing materials like thermo-set resins and adhesives to producing food and beverage products, industrial processes often require temperature control to maintain efficiency and ensure quality. Industrial heaters are necessary, but temperature controllers are the key.

There’s more than one way to control the temperature of industrial heaters. The system's operating priorities determine the approach selected. Simple voltage control can be used when operating costs are the primary consideration and less precise temperature control is tolerable.

By regulating the voltage powering the heating element, the power consumption of the heater can be controlled, and the heat output can vary. Changes in voltage can be implemented quickly, producing corresponding temperature changes, but with a lag that varies with system design. Reducing the voltage will reduce energy costs and lower the temperature. Still, the reaction time for temperature reductions can be too long for many processes, and it can be difficult to control the temperature precisely.

Beyond basic voltage control

For many applications, basic voltage control is inadequate. In those cases, designers can use on/off control, cycle control, optimum cycle control, or phase control (Figure 1). Each of those techniques presents a different set of performance characteristics:

• Phase control provides the best controllability response with good solution size and cost, plus acceptable noise performance for most applications.
• Cycle control provides good controllability response, solution size and cost, and excellent noise performance. In “optimum” cycle control, the switching status is determined for every half-cycle.
• On/off control using solid state relays (SSRs) provides good controllability response with the smallest solution size, reasonable cost, and excellent noise performance.

Figure 1: Power switching options for industrial heater control. (Image source: Omron)

Implementing phase control and optimum cycle control

Omron offers designers several options for implementing on/off control, phase control, or optimum cycle control, including the model G3PW-A245EU-S, that’s rated for operating voltages from 100 V_AC to 240 V_AC; other models are available for operation from 400 V_AC to 480 V_AC.

These controllers include heater burnout detection for increased system uptime. An RS-485 communication port is used to set variables and monitor load current.

The G3PW controllers support total runtime monitoring and are suited for use with constant resistance and variable resistance loads.

Multi-channel power controllers

The G3ZA multi-channel power controller series adds three-phase optimum cycle control to support three-phase heaters. When used with zero-cross SSRs, it supports low-noise power operation. One controller can control up to 8 SSRs. In addition, a soft-start function is available for lamp heaters (Figure 2).

Figure 2: G3ZA multi-channel power controllers support three-phase optimum cycle control. (Image source: Omron)

Three-phase optimum cycle control has been added for three-phase heaters. The model G3ZA-4H203-FLK-UTU is rated for operation from 100 V_AC to 240 V_AC and includes RS-484 connectivity. Other models are available for operation from 400 V_ACto 480 V_AC.

Temperature controllers for system integration

Temperature controllers like the EJ1N-TC4A-QQ can connect to power controllers like the G3ZA series of multi-channel controllers. They have inputs for temperature sensors as well as connections for the system PLC. The input unit can handle thermocouples, platinum resistance temperature detectors (RTDs), and analog inputs.

Functionality includes auto-tuning (AT) that can help implement proportional-integral-digital (PID) control. Self-tuning can be used to determine the PID constants using the step response method manually. Up to 16 temperature controllers can be connected using a single DeviceNet communication hub.

Thermo management software

EJ1N temperature controllers can benefit from using the EST2-2C-MV4 thermo support software package. This software enables editing and batch downloading parameters from a personal computer, speeding configuration and commissioning.

It also supports trend monitoring from up to 31 controllers. Parameters that can be monitored include process values (PVs), system values (SVs), manipulated values (MVs), PID parameters, and alarm on/off status.

Supported logic operations include setting inputs from external inputs (event inputs) or temperature status, sending values to external control or auxiliary outputs, and changing the operating state with on/off delays.

Improved PID

PID control can be highly useful for temperature control applications. Power controllers like the G3ZA series of multi-channel controllers with fast-switching SSRs, together with temperature controllers using PID algorithms, can provide the fine-grained control needed to maintain the required temperature tolerances.

Basic PID control involves a tradeoff between rapidly achieving the SV of operation with a measurable amount of overshoot or minimizing overshoot but with a slower ramp-up to the SV. In addition, there’s a tradeoff between achieving the SV and responding to disturbances in the actual PV as measured by a sensor. Better response to PV changes is often associated with poor SV ramp-up performance.

To address those performance tradeoffs, Omron has developed an enhanced PID algorithm called 2-PID, or two degrees of freedom PID. The factory PID presets are suited for most heating applications and support responses with minimal overshooting. However, with 2-PID, designers can set the reaction speed to changes in the SV, and the controller automatically tunes the PID algorithm to provide an optimized response to disturbances in PV (Figure 3).

Figure 3: Omron 2-PID temperature control (bottom graph) combines good disturbance response (right side) with good step response (left side). (Image source: Omron)

2-PID control is included in Omron’s E5CC temperature controllers, like the E5CC-QX3A5M-003. These controllers can also implement basic on/off control for less demanding applications.

The large white PV display shows the PV and the smaller green SV display shows the desired value (Figure 4). The optional CX-Thermo management software supports fast programming. For simple applications, these controllers can implement timer functions and basic logic operations with the intervention of a PLC.

Figure 4: E5CC temperature controllers clearly display PV and SV values. (Image source: DigiKey)

The RS-485 interface supports Modbus communication or Omron’s proprietary CompoWay/F. These controllers accept a variety of inputs, including:

• 12 types of thermocouples
• PT100 or JPt100 RTDs
• 4 to 20 mA or 0 to 20 mA current inputs
• 1 to 5 V, 0 to 5 V, or 0 to 10 V voltage inputs

Adaptive PID for disruption suppression

The NX-TC Adaptive Temperature Controllers take PID control to the next level and can adapt to real-time operating conditions. Adaptive control enables self-optimization of control settings due to process changes. In addition, these controllers include built-in functions for packaging sealing applications and water-cooled plastic extruders. For simple applications, basic on/off control can be implemented.

The disturbance suppression function (DSF) works in conjunction with the PID control to suppress temperature drops caused by routine and anticipated disturbances in applications like:

• Deposition equipment where the chamber temperature falls when gas is injected or material is added or removed through an open door
• Wafer probers when current is applied to the wafer, resulting in an increase in temperature
• Molding systems where the mold temperature drops when resin is injected

DSF automatically suppresses positive and negative temperature excursions caused by foreseeable events. DSF is initiated by trigger signals prior to the disturbance and adds to or subtracts from the MV. This autotuning adjusts the feed forward (FF) MV, FF operation time, and FF waiting time and can shorten the time for achieving temperature stabilization by up to 80 percent (Figure 5).

Figure 5: DSF-enhanced PID control can reduce the wait time for temperature stabilization by up to 80 percent. (Image source: Omron)

NX-TC units like the 2-channel NX-TC2405 designed for driving SSRs are optimized for scalability. Designers can use Omron’s Sysmac studio for programming control of multiple heating circuits or locations when implementing multistage heating/cooling processes.

In addition to DSF PID, these controllers support on/off control and include a heater burnout error detection function. They include EtherNet/IP and EtherCAT for network connectivity and can accept a variety of thermocouple or RTD sensor inputs.

You can’t optimize what you don’t measure

Power-switching designs, temperature controllers, and thermo management software can’t deliver optimal performance in an information vacuum. Temperature sensors provide the operational data that enables controllers and software to do their jobs. There’s a wide array of temperature sensor technologies available to designers, including:

• Thermistors function as temperature-sensitive resistors. They typically have repeatability and stability of about ±0.1°C. Model E52-THE5A-0/100C has an operating temperature range of -50°C to 300°C.
• A Type K temperature sensor is a thermocouple containing chromel and alumel conductors. They can be configured as immersion sensors, surface sensors, or other styles. Model E52-CA1GTY 2M has an operating temperature range of 0°C to 300°C.
• RTD sensors are highly accurate, and their immunity to electrical noise makes them suitable for harsh industrial environments. The E52-P6DY 1M platinum pt100 RTD sensor is rated for operation from -50°C to 250°C.
• Non-contact infrared (IR) sensors like the ES1-LW100-N can measure temperatures of a 35 mm diameter target area at a distance of 1,000 mm. It’s specified for temperatures up to 1,000°C.

Tying it together into a system

Designers of small- to medium-sized machines with up to 320 I/Os can turn to CPE2 Series PLCs from Omron. The communication capabilities of these small PLCs support machine-to-machine (M2M) data transfers and integration into the Industrial Internet of Things (IIoT).

With an operating temperature range of -20°C to +60°C, CPE2 PLCs are suited for various industrial applications like packaging and sealing machines, filling and capping machines, metal or plastic machining tools, plastic molding machines, and small part assembly. Model CP2E-N30DR-D has 18 inputs and 12 outputs and can operate from 100 to 240 V_AC or 24 V_DC power. It can be paired with the NB7W-TW01B 7” color touchscreen HMI for a complete system solution (Figure 6).

Figure 6: Omron CP2E-N30DR-D controller and NB7W-TW01B 7” color touchscreen HMI. (Image source: Omron)

Conclusion

Managing heat is an essential aspect of many industrial processes. That requires selecting and integrating power controllers and heater controllers with optimized algorithms. Temperature sensors are another important piece of the heat management puzzle. Finally, designers can turn to small PLCs to support M2M communication and integration into the IIoT.