The **250-R8** typically refers to a specific model of an **Electronic Liquid Level Controller** or a **Conductivity Relay**, commonly used in industrial pump control and tank management. These devices are designed to detect levels of conductive liquids to prevent overflow or dry-running. --- ### 1. Core Technical Specifications The 250-R8 acts as a switch based on the resistance detected between electrodes. | Feature | Specification (Typical) | | :--- | :--- | | **Input Voltage** | 120V AC or 240V AC (Model dependent) | | **Control Logic** | Single-level or Differential (Pump up/down) | | **Output Contacts** | SPDT (Single Pole Double Throw) | | **Contact Rating** | 10A @ 120/240VAC | | **Sensitivity Range** | Fixed or Adjustable (k-ohms) | | **Enclosure Type** | 8-pin Plug-in (Octal Base) | --- ### 2. Key Electronic Components Internally, the 250-R8 consists of several critical electronic sections that allow it to function safely and accurately: #### A. Power Supply Section * **Transformer:** Steps down the line voltage (120/240V) to a low-voltage AC level for the sensing circuit. This provides galvanic isolation for safety. * **Rectifiers/Regulators:** Converts AC to DC to power the internal logic and the output relay coil. #### B. Sensing Circuitry * **AC Probe Voltage:** Unlike DC sensors, the 250-R8 uses a low-voltage **AC signal** on the probes. This is crucial because it prevents **electrolysis** (buildup/corrosion) on the metal electrodes. * **Comparator/Op-Amp:** Monitors the current flow between the "Common" probe and the "High/Low" probes. When the liquid touches the probe, the resistance drops, triggering the circuit. #### C. Output Section * **Electromechanical Relay:** The "R8" designation often refers to the **8-pin relay base**. The relay physically opens or closes a high-power circuit to start or stop a pump or valve. * **LED Indicator:** Most models feature a diagnostic LED to indicate whether the relay is energized. --- ### 3. Pinout Configuration (8-Pin Octal) The standard wiring for an 8-pin level controller like the 250-R8 generally follows this pattern: | Pin Number | Function | | :--- | :--- | | **2 & 7** | Power Input (Supply Voltage) | | **1, 3, 4** | SPDT Relay Contacts (Common, NO, NC) | | **5** | High Level Probe | | **6** | Low Level / Reference Probe | | **8** | Common / Ground Probe | --- ### 4. Application Logic The 250-R8 is versatile and can be wired for two primary modes: 1. **Drain (Pump Down):** The relay turns on when the liquid reaches the High probe and stays on until it drops below the Low probe. 2. **Fill (Pump Up):** The relay turns on when the liquid drops below the Low probe and stays on until it reaches the High probe. ---