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Solid State Relays (SSRs) are electrical switching devices that serve the same purpose as electromechanical relays but without the moving parts hence the name 'solid state'. They represent an alternative to traditional electromechanical relays, eliminating mechanical components to deliver a more reliable, durable, and efficient performance.

Unlike electromechanical relays that use physical movements to initiate switches, SSRs utilise the electrical and optical properties of semiconductors. This technology enables quicker switching times and reduces potential wear and tear, extending operational longevity.

RS offers a comprehensive selection of high-quality solid state relays from industry-leading brands like Celduc, Sensata/Crydom, Omron, and Phoenix Contact. With advanced features such as zero voltage turn-on and zero current turn-off, SSRs ensure minimal electrical noise and transients, enhancing their suitability for various applications.

**Key Advantages:**

- **Durability:** No moving parts to wear out, eliminating mechanical degradation.
- **Efficiency:** Capable of switching on and off faster than mechanical relay arms.
- **Reliability:** Reduces electrical noise and provides stable performance.

## **Applications of Solid State Relays**

Solid State Relays are pivotal in various industrial and technological settings, offering versatile applications due to their robust performance. Here are some common uses:

- **Industrial Control Systems:** Enhances automation and process efficiency.
- **Robotics:** Provides reliable switching for precise robotic operations.
- **Medical Equipment:** Ensures dependable operation in sensitive medical applications.
- **Data Acquisition Systems:** Facilitates accurate data handling and processing.
- **Power Management:** [Controls power delivery in systems](https://sg.rs-online.com/web/content/discovery/ideas-and-advice/relay-systems-for-energy-management-smart-solutions-for-efficiency) requiring high reliability, such as lighting and heating systems.

## **Mounting Options for Solid State Relays**

Choosing the right mounting option for Solid State Relays (SSRs) is crucial to ensure optimal performance and integration in various applications. Here’s an overview of the primary mounting types available:

### **1. PCB Mount**

PCB-mount solid state relays are designed for direct attachment to printed circuit boards (PCB), offering a streamlined and efficient installation. These relays are ideal for incorporation into motherboards and similar PCB applications, available with push-in pin fittings or requiring soldering to the PCB surface. This mount type is particularly beneficial for applications where space is at a premium and a low-profile installation is necessary.

### **2. DIN Rail Mount**

DIN-mount SSRs are tailored for attachment to standard DIN rails, commonly found within industrial control panels and enclosures. This mount facilitates easy installation and access, making it perfect for environments where multiple control components need to be housed together efficiently. The universal compatibility with DIN rail setups ensures these SSRs can be easily integrated into existing systems.

### **3. Panel and Chassis Mount**

Panel-mount SSRs are versatile and widely used, designed to be installed flush with various types of industrial panels, hatches, or heatsinks. Chassis-mount variants offer similar benefits, providing robust attachment options. Both types typically use screw fittings through the SSR base, body, or purpose-designed eyelets, ensuring secure and reliable mounting in a variety of applications.

### **4. Heatsink Mount**

[Heatsink-mount SSRs](https://sg.rs-online.com/web/content/discovery/ideas-and-advice/heatsinks-guide) allow for the attachment of a cooling solution, which is crucial for managing the heat generated by the relay during operation. Depending on the application's environmental demands, these mounts support both passive and active cooling options. This feature is vital for maintaining performance and longevity in high-power or thermally challenging conditions.

### **5. Plug-In Mount**

Plug-in SSRs are designed for rapid and convenient setup, embodying plug-and-play functionality. These are particularly useful for applications requiring frequent reconfiguration or where ease of maintenance is a priority. The specific type of plug used is determined by the intended insertion environment, typically geared towards seamless integration into PCBs or similar assemblies.

Each mounting option is engineered to meet specific operational needs and environmental conditions, ensuring that regardless of the setup, an SSR is available to meet the application's demands.

## **Switching Types of Solid State Relays**
- **AC Output SSRs:** These SSRs are designed to switch AC loads, both resistive (e.g., heaters, lamps) and inductive (e.g., motors, solenoids). They typically use thyristors or back-to-back SCRs as the switching element.
- **DC Output SSRs:** DC output SSRs are used to control DC loads like DC motors, electromagnets, and DC-powered equipment. They often employ power MOSFETs or bipolar transistors as the switching device.
- **AC/DC Input SSRs:** These SSRs can accept either AC or DC control signals, making them versatile for various applications. The input circuitry is designed to handle both AC and DC voltages.
- **Zero Cross SSRs:** Zero cross SSRs switch the load only when the AC waveform crosses zero, minimising electromagnetic interference (EMI) and electrical stress on the load. They are suitable for resistive loads like heaters.
- **Random Fire SSRs:** Random fire SSRs can switch the load at any point in the AC cycle, making them suitable for inductive loads like motors and solenoids. However, they generate more EMI compared to zero cross SSRs.

## **Selecting the Right SSR**

Choosing the appropriate SSR for an application involves matching its ratings to the load requirements and considering factors like load type, ambient temperature, and switching frequency. Here are some key considerations:

- **Load Requirements** - Ensure that the SSR's load voltage, current, and power ratings are suitable for the intended load. It's generally recommended to select an SSR with a higher rating than the maximum expected load to provide a safety margin.
- **Load Type** - Different types of loads (resistive, inductive, capacitive) may require specific SSR configurations or additional protection devices like snubbers or varistors.
- **Ambient Temperature** - The ambient temperature in the installation environment affects the SSR's ability to dissipate heat. Higher temperatures may necessitate derating the SSR or using additional cooling measures.
- **Heat Sinking** - Proper heat sinking is crucial for SSRs handling higher load currents or operating in elevated ambient temperatures. Manufacturers often provide guidelines for heat sink selection and mounting.
- **Input Control Signal** - The SSR's input control voltage and current requirements must be compatible with the control system or PLC used to trigger the SSR.
- **Switching Frequency** - Applications involving high-frequency switching or PWM control may require SSRs with faster turn-on and turn-off times.

## **Delivery Information**

For prompt delivery of SSRs and related items such as [safety switches](https://sg.rs-online.com/web/c/switches/safety-interlock-switches-components/non-contact-safety-switches/) and [electricity relays](https://sg.rs-online.com/web/c/relays-signal-conditioning/relays/power-relays/) across Singapore, RS offers next-working-day delivery on all online orders placed from Monday to Friday before 3:30 pm, assuming the products are in stock. For detailed information on all available delivery options, including offline purchases and combined shipping, please visit our [delivery information page](https://sg.rs-online.com/web/content/support/all-articles/delivery).



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