PLC control cabinet (Programmable Logic Controller) is the automation brain of an entire industrial refrigeration system, from cold storage rooms to IQF freezing lines. It receives signals from temperature, pressure and flow sensors, then processes them according to the programmed logic to control compressors, evaporators, condensers and the other actuators in the system.
Tan Long specialises in designing and building PLC control cabinets for industrial refrigeration systems from 500 kW to over 3,000 kW (≈ 1,700,000 BTU/h), using controllers from Siemens, Mitsubishi, LS and Schneider. All Tan Long PLC cabinets comply with IEC 60439-1:2004 and are manufactured at our Tay Ninh plant (formerly Long An) with CNC laser cutting and protective powder coating.
This page covers the definition of a PLC, the cabinet construction, the operating principle, real applications in NH3 and Freon refrigeration systems, the technical specifications, the Tan Long delivery process, and the technical questions operating engineers ask most often.
What is PLC control cabinet?
A PLC control cabinet is an electrical system with an integrated programmable logic controller (PLC) that fully automates the operation of industrial machinery according to a pre-programmed scenario. PLC stands for Programmable Logic Controller, a controller whose logic can be reprogrammed. Unlike traditional mechanical relays, a PLC changes its control algorithm entirely in software with no hardware change. The operator monitors and adjusts parameters through an HMI (Human-Machine Interface) touch screen on the cabinet itself.
In industrial refrigeration, a PLC cabinet handles dozens of control loops at once: switching compressors on and off according to the actual cooling load, adjusting condenser fan speed through an inverter, monitoring store temperature by zone from -25°C to +15°C, and raising an alarm when suction or discharge pressure exceeds the safe threshold. This multi-loop capability is what distinguishes a PLC from simple controllers such as a thermostat or a mechanical timer.
Electronic control
Applications of the PLC cabinet in industrial refrigeration systems
PLC control cabinet supplied by Tan Long acts as the central operating authority and is widely used in 5 key types of industrial refrigeration system:
- Multi-temperature cold storage rooms: This is the most common application of the PLC control cabinet. One central control system can manage several zones simultaneously: freezer rooms (-25°C to -18°C), chill rooms (+2°C to +5°C) and preparation rooms (0°C to +10°C). The PLC distributes the cooling load automatically, prioritising the most important zones when compressor capacity fluctuates, so product quality in the cold store stays consistent.
- Air blast freezer systems: For wind tunnel, PLC control cabinet is programmed for a batch freezing cycle. The system strictly controls the rapid pull-down from +10°C to -18°C in a short time (3 to 6 hours), then switches automatically to storage mode once the product core reaches the requirement. Tan Long has proven this capability by installing PLC systems for 6 air blast freezing tunnels at the Frescol Tuna Vietnam project.
- High-speed IQF belt freezers: PLC control cabinet in a mesh belt IQF freezer system requires complex coordination between belt speed and freezing chamber temperature (-35°C to -40°C). The PLC handles more than 200 I/O points simultaneously to control the outlet product temperature and trigger the evaporator defrost cycle automatically without interrupting the production line, optimising the operating process for the business.
- Refrigeration systems using NH3 (ammonia): In NH3 refrigeration systems, the PLC control cabinet includes strict safety protection circuits. The system continuously monitors the NH3 concentration in the air through gas detectors (alarm at 25 ppm, emergency shutdown at 150 ppm) and controls the safety valves and the ventilation system. Tan Long has delivered this solution successfully for major partners such as Kyokuyo Vina Foods, Lotte F&G and C.P. Vietnam, ensuring the highest level of safety in operating and servicing refrigeration systems.
- Industrial water chillers:PLC control cabinet applied in a water chiller system holds the outlet water temperature precisely between +3°C and +12°C. Through a rotation algorithm, the PLC balances the running hours between the refrigeration compressors, extending equipment life and helping technicians keep operating logs for effective predictive maintenance.
PLC cabinet compared with SCADA cabinet
PLC cabinets and SCADA cabinets serve two different levels of control in an industrial refrigeration system. Understanding the difference correctly helps you choose the solution that matches your scale and budget.
| Criteria | PLC electrical cabinet | SCADA cabinet |
|---|---|---|
| Main functions | Local automatic control | Remote monitoring and control over the network |
| Monitoring scope | 1 system or 1 area | Several systems across the whole plant |
| User interface | HMI screen on the cabinet (7–12 inch / 17.8–30.5 cm) | Central computer, large 27–55 inch screen (68.5–139.7 cm) |
| Data storage | Limited to the PLC memory | Server storing long-term history (years, decades) |
| Remote connection | No (or limited) | Yes, over Ethernet, VPN or 4G |
| Suitable for | Single systems, small plants | Large plants, several areas, central reporting needed |
| Investment costs | Lower | Higher (30–50%) |
Tan Long supplies both solutions and advises combining them: the PLC handles local control in real time while SCADA collects data and gives a plant-wide overview. This is the common architecture in large seafood and food plants in Vietnam. See also: SCADA control cabinet.
Construction of the Tan Long PLC control cabinet
PLC control cabinet designed and installed by Tan Long comprises 6 main component groups. Each group has an independent function but works closely with the others to run the entire industrial refrigeration system automatically and accurately.
- Durable enclosure and mechanical structure: The enclosure is made from 1.5 mm CT3 steel for standard cabinets, or SUS 304 stainless steel for high-humidity or chemically exposed environments such as seafood processing areas. The PLC control cabinet size is flexible, from 600 x 800 x 200 mm for small systems to 1,000 x 2,000 x 600 mm for large systems above 500 kW. The IP54 protection rating resists dust and water effectively, making installation safe in the machine rooms of food plants.
- Central PLC controller (the system brain): This is the core component of the PLC control cabinet. Tan Long prefers well-known PLC ranges from Siemens (S7-300, S7-1500), Mitsubishi (Q series, FX5U), LS (XGI, XGB) and Schneider (Modicon M340) depending on the scale of the project. For example, the Siemens S7-1500 has an extremely fast processing speed (1 ns per instruction) and supports up to 8,192 I/O points, making it the optimal choice for large-scale cold storage systems such as the 12,000 MT store project at Frescol Tuna Vietnam.
- I/O modules for receiving and transmitting signals: Input modules receive signals from peripheral devices such as Pt100/Pt1000 temperature sensors, 4 – 20 mA pressure sensors, pressure switches (pressostats) and flow switches. After processing, output modules send control commands to contactors, industrial refrigeration, solenoid valves and the indicator light system. A typical 500 kW refrigeration system needs 64 to 128 I/O points to run smoothly.
- HMI operating interface: The HMI screen in the PLC control cabinet displays the system P&ID diagram in real time. Through this interface, engineers monitor the temperature of each zone, the suction and discharge pressure of the refrigeration compressors and retrieve the fault log. Tan Long usually fits quality screens such as the Weintek MT8000 (7 inch) or the Siemens KTP1200 (12 inch) for the clearest control experience.
- Protection and power distribution devices: For safe operation, the system is fully equipped with a 3-phase main breaker (MCCB), an earth leakage breaker (ELCB), thermal overload protection relays and an EMC filter. These components are imported from specialist brands such as ABB, Schneider and LS. This protection system minimises electrical risk and keeps operating and servicing the refrigeration system safe for the business.
- Inverter for energy optimisation: An essential part of modern PLC control cabinet lines is the inverter, which adjusts the speed of the condenser fan motors and the cooling pumps. This saves 20% to 40% of electricity compared with traditional fixed-speed operation. Tan Long installs inverters from Mitsubishi, Delta and Danfoss, giving customers a fast return on investment.
Technical standards applied to the PLC control cabinet
Equipment supplied by Tan Long is manufactured to the following standards and material requirements:
- ISO
- IEC 60439
- IEC
- SUS 304 stainless steel
- NH3 refrigerant
- Freon refrigerant
- IP protection rating
Depending on each project's requirements, the engineering team will advise on the material configuration and connection standards that best suit the plant's existing system.
The Tan Long PLC cabinet design and delivery process
Tan Long manufactures the PLC control cabinet through a strict standardised 6-step process, ensuring consistency from the site survey through to handover for live operation.
- Step 1: Survey existing conditions and establish technical requirements: Tan Long engineers survey the site directly to collect the list of equipment to be controlled, including refrigeration compressors, pumps, fans and solenoid valves. This stage is critical for determining the number of I/O points, selecting the right PLC range and analysing specific safety requirements, particularly for refrigeration systems using NH3.
- Step 2: Detailed electrical drawing design: Based on the survey data, Tan Long prepares the electrical schematic, the equipment layout drawing inside the cabinet and the control algorithm flowchart. The customer takes part in approving the design drawings PLC control cabinet to ensure they match the intended function before manufacturing begins.
- Step 3: Assembly and wiring at the Tan Long plant: Enclosure and equipment assembly takes place at the Tan Long plant (Duc Hoa 1 Industrial Park, Tay Ninh). All wiring follows the IEC 60446 colour standard. Before despatch, every control circuit in the PLC control cabinet undergoes a continuity test and an insulation resistance (IR) test at a minimum of 500 V.
- Step 4: PLC programming and HMI interface design: Automation engineers write the code in Ladder Diagram or Function Block Diagram. After loading the program into the PLC, Tan Long runs a simulation with simulated signals to check every operating scenario and fault handling path, confirming the software works before physical installation.
- Step 5: Installation and commissioning: Once delivered to the electrical room, engineers connect the field cabling and carry out a no-load test run. Next comes live load running of the entire cold store system or IQF belt freezer, to tune the setpoints optimally to the customer actual production.
- Step 6: Operator training and technical documentation handover: Tan Long runs in-depth training for the customer technicians on using the HMI screen and dealing with common faults. The handover package includes as-built drawings, the PLC programming documentation and equipment test certificates. This leaves the customer fully self-sufficient and keeps operating and servicing the refrigeration system safe over the long term.
Technical specifications of PLC control cabinet
To keep the refrigeration system running stably in harsh industrial environments, every PLC control cabinet at Tan Long complies with strict technical standards. Below is the standard specification table for the control cabinet lines:
| Parameter | Standard value |
|---|---|
| Supply voltage | 380 V – 3 pha – 50 Hz (±10%) |
| Control circuit voltage | 24 VDC |
| Enclosure protection rating | IP54 (standard), IP65 (optional) |
| Operating temperature | -10°C to +55°C (14°F to 131°F) |
| Enclosure material | CT3 steel, SUS 201 and SUS 304 stainless steel |
| Enclosure manufacturing technology | CNC laser cutting, CNC bending, powder coating |
| PLC controller | Siemens, Mitsubishi, LS, Schneider (to requirement) |
| HMI screen | Weintek, Siemens (7 inch – 12 inch / 17,8 cm – 30,5 cm) |
| Inverter | Mitsubishi, Delta, Danfoss |
| Manufacturing standard | IEC 60439-1:2004 |
| Standard for assembled devices | ISO 9001-2008 |
| Warranty | 12 months |
The cabinet size depends on how much equipment is fitted inside. A PLC cabinet for a 2–4 compressor system is usually 800 × 1,800 × 500 mm (W×H×D). A PLC cabinet with integrated SCADA for a large plant system can reach 1,200 × 2,200 × 800 mm.
Why choose Tan Long to supply your PLC control cabinet?
Tan Long is a refrigeration engineering joint stock company with more than 20 years in industrial refrigeration, serving seafood and food processing plants and large-scale cold stores across Vietnam.
- In-house manufacturing: its own factory in Duc Hoa 1 Industrial Park, Tay Ninh (formerly Long An), with no dependence on outside subcontractors.
- Turnkey D&B capability: design and construction under one roof, reducing the risk of a gap between the drawings and what is actually installed.
- Complete documentation: equipment is handed over with technical files and CO/CQ certificates of origin.
- Engineers with field experience: advice based on each plant's actual system configuration rather than selling from a catalogue.
- Support after handover: the technical team is on hand for operation and maintenance throughout the equipment's life.
For advice on a specific configuration, please contact Tan Long's engineering team or see the projects already delivered.
How the PLC control cabinet works in a refrigeration system
PLC control cabinet operates on a closed logic loop comprising three stages: reading signals, processing the algorithm and writing the outputs. The system scan cycle is extremely fast, just 1 ms to 10 ms depending on the hardware configuration, so every change in temperature or pressure is handled instantly.
Specifically, in industrial refrigeration systems the control process of the PLC control cabinet runs through 4 core steps:
- Input scanning: First, the I/O modules of the PLC control cabinet continuously update the status from the sensor system. This data includes the cold store temperature from Pt100 sensors, suction pressure from 4 – 20 mA sensors, compressor oil level from a float switch and the open/closed status of the solenoid valves.
- Central processing: At this step, the PLC CPU compares the measured values with the programmed setpoints. For example, if the store is set to -18°C but the actual temperature rises to -16°C, the CPU immediately calculates and commands an additional compressor to start to make up the cooling shortfall.
- Output control: After processing the logic, the PLC control cabinet sends signals to the actuators. It closes the contactor to start the refrigeration compressor, opens the liquid feed solenoid valve and switches on the evaporator fans in a carefully calculated time sequence. This keeps operation stable and avoids electrical shock from a sudden inrush current.
- Feedback monitoring and safety protection: The system monitors feedback continuously. If it detects abnormal parameters such as discharge pressure above 18 bar (261 PSI) or an excessively high compressor discharge temperature, the PLC control cabinet shuts the system down automatically and raises an alarm. This is a mandatory procedure to ensure Safety in operating and repairing refrigeration systems, helping the business avoid serious equipment damage.
Optimising performance with the PID algorithm One strength of the Tan Long PLC control cabinet is its use of PID (Proportional-Integral-Derivative) control. This algorithm allows fine modulation of the electronic expansion valve (EEV) to hold suction superheat at the optimal 5°C (41°F). Compared with systems using an ordinary thermostatic expansion valve (TXV), the PLC-integrated solution improves cooling performance significantly and extends the life of the whole plant.
Why choose a PLC control cabinet from Tan Long?
With more than 20 years of experience in industrial refrigeration, Tan Long has established itself as a specialist by treating the PLC control cabinet as the core brain of every project. Quite unlike purely domestic electrical contractors, Tan Long engineers understand the thermal and refrigeration process from the inside. That lets Tan Long go beyond assembling equipment to optimising in-depth control algorithms, so the system runs accurately and saves the maximum energy.
Tan Long products are manufactured at our own plant in Duc Hoa 1 Industrial Park, Tay Ninh. With a capacity of 50 to 80 cabinets a month, production there is strictly controlled to ISO 9001-2008, combined with CNC machining and modern welding robots for durability. Customer confidence also comes from the large real projects Tan Long has delivered successfully:
- 12,000 MT cold storage system: Installed at the Frescol Tuna Vietnam project (Nghe An).
- Complete NH3 refrigeration system: Delivered for Lotte F&G Vietnam in Tay Ninh to demanding safety standards.
- High-speed freezing line: Integration PLC control cabinet for the IQF belt freezer system at Kyokuyo Vina Foods.
- Compressor set control: Running 4 to 12 large refrigeration compressors simultaneously, from 75 kW to 315 kW per set.
Tan Long - Prestigious electrical cabinet supplier
Alongside delivery capability, Tan Long pays particular attention to after-sales service to keep production continuous. The technical team supports customers Monday to Saturday, with a commitment to respond within 4 hours for emergencies. Every 6 months, Tan Long provides in-depth maintenance including connection checks, firmware updates and control program backups. This is our highest commitment to keeping operating and servicing the refrigeration system safe for the business.
For advice and the most accurate quotation for a PLC control cabinet for your cold store or processing plant project, please send us the equipment list, the system capacity and the P&ID diagram if available. Tan Long is always ready to work with you through these channels:
- Headquarters: 86 Dong Den, Ward 14, Tan Binh District, Ho Chi Minh City.
- Factory: Lot MM3-2, Road No. 04, Duc Hoa 1 Industrial Park, Tay Ninh.
- Technical advice hotline: (+84) 933 357 058 (Mr. Thinh) or (+84) 982 330 357 (Mr. Sang).
- E-mail: info@tanlongvn.com.
- Working hours: Monday to Saturday (8:00 – 17:30).
Frequently asked questions about PLC control cabinets
How does a PLC cabinet differ from an ordinary relay cabinet?
A relay cabinet uses mechanical relays with physical contacts to switch circuits according to fixed wiring. Changing the control logic means rewiring. A PLC cabinet replaces all the control relays with a program in memory. Changing the control logic only means editing the software, with no hardware change. A PLC cabinet takes 60–70% less space than a relay cabinet with the same function and is more reliable because there are no mechanical contacts to wear.
How long does it take to build a PLC cabinet?
A PLC cabinet for a medium refrigeration system (2–4 compressors, 64–128 I/O points) takes 3 to 5 weeks from contract signing to despatch. Commissioning on site adds 3–7 days depending on the complexity of the refrigeration system. A PLC cabinet for a system above 500 kW with integrated SCADA needs 6–10 weeks. Tan Long provides a detailed stage-by-stage schedule at contract signing.
Which PLC brand suits an NH3 refrigeration system best?
Tan Long prefers the Siemens S7-300 and S7-1500 for large NH3 refrigeration systems because of their fail-safe PLC programming to IEC 62061 and SIL 2, which brings the system to a safe state automatically on a hardware fault. The Mitsubishi Q Series suits medium systems (2–6 compressors), at 15–25% lower cost than Siemens while still meeting the control requirements of standard Freon and NH3 refrigeration systems.
Can a PLC cabinet integrate with an existing SCADA system?
Yes. New Tan Long PLC cabinets support the Modbus RTU, Modbus TCP/IP, Profibus DP and OPC-UA protocols, compatible with most SCADA systems running in Vietnam such as Wonderware, iFIX and Vijeo Citect. Tan Long engineers perform the tag mapping between the new PLC and the existing SCADA, with no need to replace the SCADA software.
Roughly what does annual PLC cabinet maintenance cost?
Periodic maintenance cost depends on the size of the system. A PLC cabinet for a 200–500 kW refrigeration system is maintained twice a year at roughly 5–10 million VND per visit, covering electrical contact checks, cabinet cleaning, PLC backup battery checks, program backup and firmware updates. The PLC backup battery (3V lithium) is replaced every 2–3 years at 150,000 to 500,000 VND depending on the model. Tan Long offers an annual maintenance contract with priority 24-hour response and a 10% discount on replacement parts.
Where in a refrigeration plant is the PLC cabinet installed?
The PLC cabinet is installed in a control room held between 20°C and 30°C (68°F to 86°F), separate from the compressor room and high-humidity areas. It is mounted on a flat surface with at least 800 mm (31.5 inch) clearance in front for maintenance access. A SUS 304 stainless steel PLC cabinet can be installed in wet areas such as a preparation room, provided no water is sprayed directly at it.
Request advice and a quotation
Tan Long designs and builds industrial refrigeration equipment at its plant in Duc Hoa 1 Industrial Park, Tay Ninh (formerly Long An), so capacity and dimensions can be adjusted to the actual site. Call 0933 357 058 (Mr. Thinh) or send a quotation request with your output per shift and your main product type.
