YOKOGAWA ET5*B Signal Conditioner – STARDOM Series

YOKOGAWA ET5*B – Thermocouple Input Signal Conditioner with 3-Way Galvanic Isolation

The YOKOGAWA ET5*B is a precision thermocouple (T/C) input signal conditioner engineered for continuous-duty process measurement loops where signal integrity, ground-loop elimination, and long-distance transmission accuracy are non-negotiable. Positioned within YOKOGAWA’s STARDOM field control architecture, this module converts millivolt-level thermocouple EMF signals into a stable, linearly scaled 4–20 mA or 1–5 V DC analog output, fully isolated from both the power rail and the downstream control system. Its compact DIN-rail form factor and universal T/C type compatibility make it a standard-fit component across refinery, chemical, power generation, and heavy manufacturing instrumentation panels.

Unlike passive signal splitters or simple barrier devices, the ET5*B performs active cold-junction compensation (CJC) internally, correcting for ambient temperature drift at the terminal block without requiring an external reference junction. This is critical in cabinet environments where internal temperatures fluctuate with seasonal load cycles. The module’s linearization engine maps the non-linear Seebeck coefficient curves of each supported thermocouple type to a linear output span, delivering ±0.1% of span accuracy across the full operating range.

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Technical Parameters

Hardware Logical Analysis

The ET5*B’s internal architecture is structured around three discrete functional blocks separated by transformer-coupled isolation barriers: the input acquisition stage, the signal processing core, and the output driver stage.

Input Acquisition Stage: The thermocouple terminals feed into a high-impedance differential amplifier with an input impedance exceeding 1 MΩ, preventing source loading on the low-energy thermocouple circuit. A precision instrumentation amplifier with programmable gain handles the microvolt-to-millivolt signal range inherent to T/C sensors. An integrated cold-junction sensor (typically a platinum RTD or bandgap reference IC) mounted at the terminal block measures the reference junction temperature in real time, and its output is summed algebraically with the T/C EMF before linearization — this is the hardware implementation of the Seebeck equation correction.

EMC Design: The module employs multi-layer PCB construction with dedicated ground planes separating the analog input section from the DC/DC converter switching node. Ferrite bead filters on the power input lines attenuate conducted emissions in the 150 kHz–30 MHz band. The isolation barrier capacitance is kept below 10 pF to minimize common-mode noise coupling from the process field side — a critical parameter in environments with variable-frequency drives (VFDs) or high-current bus bars in proximity.

Linearization Engine: A fixed-function DSP or microcontroller executes the IEC 60584 polynomial linearization coefficients for each T/C type. The lookup table approach is replaced by a piecewise polynomial evaluation, which delivers consistent accuracy across the full temperature span without the quantization steps visible in coarser table-interpolation methods. Output update rate is synchronized to the internal ADC conversion cycle, typically 50–60 Hz, providing sub-20 ms latency for process control feedback loops.

Output Driver: The 4–20 mA current loop driver is a precision voltage-to-current converter with a compliance voltage headroom of at least 3 V, ensuring linearity is maintained even at maximum loop resistance. An internal clamp circuit limits output to 21 mA under fault conditions, protecting downstream AI modules from overrange damage. Open-circuit detection on the output loop is supported in select sub-models, generating a diagnostic flag readable by the host controller.

System Integration Benefits

• Ground Loop Elimination: The 3-way isolation architecture breaks all conductive paths between the thermocouple circuit, the 24 V DC supply bus, and the analog input card of the PLC or DCS. This prevents circulating ground currents — a primary source of 50/60 Hz interference in multi-point temperature measurement systems — without requiring additional isolation barriers at the AI module.
• Direct Compatibility with Standard AI Modules: The 4–20 mA output interfaces directly with any IEC 61131-compliant analog input module, including Siemens S7-300/400/1500 SM series, Allen-Bradley 1756-IF16, Yokogawa CENTUM VP AFV10D, and Schneider Modicon X80 AMI0410. No signal conditioning at the controller end is required.
• Deterministic Signal Latency: With a fixed response time of ≤500 ms and a stable output update cycle, the ET5*B introduces a known, bounded delay into the temperature measurement loop. This is essential for PID tuning in thermal processes where derivative action is sensitive to measurement noise and latency.
• Diagnostic Transparency: Sub-models with open-circuit and over-range detection provide hardware-level fault flags that can be mapped to PLC diagnostic bits, enabling the control system to distinguish between a process excursion and a sensor or wiring fault without manual field inspection.
• Reduced Panel Wiring Complexity: By consolidating CJC, linearization, and isolation into a single DIN-rail module, the ET5*B eliminates the need for separate compensation cables, isothermal terminal blocks, and external barriers. This reduces panel wiring labor and the associated risk of wiring errors.
• Multi-Type T/C Flexibility: A single module family covers J, K, T, E, R, S, B, and N thermocouple types. Standardizing on the ET5*B across a plant reduces spare-part inventory complexity and simplifies maintenance training.
• Long-Distance Signal Transmission: Converting the T/C millivolt signal to 4–20 mA at the field junction box allows transmission over standard twisted-pair cable runs of up to 1,000 m without signal degradation — a significant advantage over direct T/C extension cable runs, which are susceptible to resistance variation and EMI pickup over long distances.
• Scalable Architecture for STARDOM FCN/FCJ: Within YOKOGAWA’s STARDOM autonomous controller architecture, the ET5*B feeds analog input modules that connect to the FCN/FCJ backplane via the Vnet/IP or FOUNDATION Fieldbus interface. The module’s stable output characteristics support the STARDOM system’s deterministic scan cycle, maintaining measurement consistency across distributed node configurations.

Quality Assurance & Global Logistics

Every YOKOGAWA ET5*B unit supplied through siemensplc.com is sourced from verified distribution channels with full batch traceability. YOKOGAWA’s manufacturing facilities operate under ISO 9001 quality management systems, and each ET5*B unit leaves the factory with calibration data traceable to national measurement standards. We do not supply refurbished, reconditioned, or grey-market units. Physical inspection covers label integrity, housing condition, terminal block quality, and serial number consistency against YOKOGAWA’s production records.

Shipments originate from our Xiamen, China operations hub, with access to DHL Express, FedEx International Priority, and air freight consolidation services. Standard in-stock orders are dispatched within 2–3 business days. Export documentation — including commercial invoice, packing list, certificate of origin, and HS code classification (HS 9032.89) — is prepared for each shipment. Customs clearance support is available for destinations requiring additional documentation. Bulk orders of 10+ units qualify for dedicated freight coordination and volume pricing.

Contact Information

📧 Email: [email protected]
💬 WhatsApp: +86 18359268345
🌐 Web: siemensplc.com
📍 Location: Xiamen, China
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