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        Triconex 3721
        Triconex 3721
        Triconex 3721
        Triconex 3721
        Triconex 3721
        Triconex 3721
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        • Lifecycle Status

          Discontinued / Obsolete by OEM
          Apter Power provides reliable, discontinued Triconex hardware to extend your infrastructure's lifecycle and avoid costly system migrations.

        3721

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        The Triconex 3721 Analog Input Module provides precise, isolated 32-point differential analog measurements with TMR operation, ideal for mission-critical industrial control systems.
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        Warranty Policy
        We provide 1 year warranty for all remaining parts.
        The warranty period is one year from the date of shipment, unless otherwise stated in the parts description. We guarantee that the project will not exhibit functional defects that may occur under normal operating conditions during the warranty period.
        Return Notice
        The warranty period is one year from the date of shipment, unless otherwise stated in the parts description. We guarantee that the project will not exhibit functional defects that may occur under normal operating conditions during the warranty period.
        In the event of a defect, we will send new equipment, repair equipment or refund the purchase price based on our availability. You must contact us to obtain a return authorization and return the defective device to us within 14 days of reporting the defect.
        Shipping Mode
        Various transportation options are available in each country. Shipping methods and fees are clearly indicated on all quotations.Various transportation options are available in each country. Shipping methods and fees are clearly indicated on all quotations.
        Parts Availability
        Apter Power offers a wide range of components, products and services related to industrial automation. We also supply new products from a variety of quality manufacturers.
        How to order
        We have been working hard to update our inventory. If we have stock or parts available for new factory purchases, you can contact the order online. If we do not currently have an inventory, the displayed quantity will show "Ask". Please create an online quote or contact us by phone, fax or email to check availability.

        Technical specifications for 3721

        • Manufacturer:
          Invensys
        • Part Number:
          3721
        • Product Family:
          Triconex
        • Product Type:
          Analog Input Module
        • Stock:
          1
        • Voltage:
          0 to 5 VDC or -5 to +5 VDC1, + 6%
        • Type:
          TMR
        • No. of Input Points:
          32 differential, DC-coupled
        • Isolated Points:
          Yes
        • Input Update Rate:
          10 ms
        • Resolution:
          12 bits or 14 bits programmable
        • Accuracy:
          < 0.15% of FSR from 0° to 60° C
        • Input Resistance (load):
          10 MΩ (DC), min.
        • Power-Off Resistance:
          140 kΩ (DC), typical
        • Common Mode Rejection:
          -85 dB (DC – 100 Hz)
        • Common Mode Range:
          -12V to +12V peak
        • Leg-to-Leg Isolation:
          420 kΩ, typical
        • Normal Mode Rejection:
          -3 dB @ 23 Hz; -8 dB @ 60 Hz; -14 dB @ 120 Hz
        • Input Overrange Protection:
          150 VDC/115 VAC continuous
        • Current Range:
          0-20 mA with 250 Ω shunt resistor
        • Diagnostic Indicators Module Status:
          PASS, FAULT, ACTIVE, FIELD
        • Color Code:
          Yellow
        • Weight:
          2.02 kg
        • Estimated shipping dimensions:
          2.1x40.8x40cm
        • Tariff Code:
          8537101190
        • Country of origin:
          USA
        • Place of shipment:
          Xiamen, Fujian, China
        By purchasing this item, you agree to the Terms & Conditions, ApterPower is not an authorized distributor for listed manufacturers or tradenames and therefore the manufacturer's warranty does not apply. All our products come with ApterPower's 1-year warranty.

        More Information

        Overview Manuals Specifications Use Cases Safety & Compliance Performance & Efficiency

        Features:

        • Differential Voltage Acquisition Interface for Triconex Safety Systems
        • Integrates TMR Signal Processing with DC-Coupled Analog Measurement
        • Functions Cooperatively with Tricon Main Processors and I/O Subsystems
        The Triconex 3721 Analog Input Module serves as the primary differential analog input interface within a Tricon rack, delivering high-integrity voltage measurement capability to all safety functions across the system. The 3721 continuously accepts differential input signals in the range of 0 to 5 VDC or –5 to +5 VDC and processes these through its triple-modular-redundant architecture to ensure fault-tolerant data acquisition. Seamless signal validation is inherent to the 3721, as each channel employs three independent paths that execute a mid-value select algorithm, thereby isolating any path that deviates beyond acceptable tolerance. The 3721 achieves substantial improvements over conventional single-channel designs by incorporating DC-coupled differential measurement within the Tricon platform.

        The 3721 provides essential analog input functions common to the entire safety loop, and is a critical component of the measurement path, directly affecting the accuracy and availability of the overall control system. One or more 3721 modules are deployed per rack depending on the required channel density and safety integrity level. The 3721 occupies a standard single slot in the Tricon rack and is installed in any available I/O slot position alongside other Triconex modules.

        For high-availability applications, the Tricon system leverages the inherent TMR architecture of the 3721 at the channel level rather than requiring a second physical module. In addition to standard triple-path operation, the 3721 configuration performs continuous diagnostics. The 3721 TMR channel architecture executes fault detection using the internal comparators specified in the module design. Using this method, the 3721 continually monitors the health of all three signal paths. If the module detects that any single path is no longer providing valid measurement data (outside configured voltage or tolerance levels), it will automatically exclude that path from the voting process, maintain accurate output using the remaining two healthy paths, and report the diagnostic status to the main processor.

        The 3721 Triconex Analog Input Module may still be available for purchase and support from Apter Power beyond End-Of-Life (EOL) by the manufacturer (OEM).
        Triconex 3721 Analog Input Module Manuals,Datasheets,Link Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.
        Triconex 3721 Analog Input Module Specs

        General

        • Manufacturer Triconex
        • Model 3721
        • Condition New Original ready stock
        • Product Family 3704E,3720,3701,3703E
        Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.
        • Nuclear Reactor Protection: Used for real-time monitoring of nuclear steam supply systems, such as in the "Heqi-1" project at the Tianwan Nuclear Power Plant, to ensure safe and efficient industrial steam supply.
        • Emergency Shutdown (ESD): Provides reliable data inputs for systems designed to safely shut down industrial processes during abnormal conditions.
        • Turbomachinery Control: Monitors critical parameters in turbines and compressors to prevent overspeed or mechanical failure.
        • Fire and Gas Detection: Reliable monitoring of environmental sensors in hazardous industrial environments.
        • Redundancy & Voting: It uses three independent "legs" of circuitry; the system votes on incoming data to identify and compensate for individual hardware faults without interrupting the process.
        • Certifications: Qualified for use in safety-critical systems by major agencies, including TÜV Rheinland and Factory Mutual (FM).
        • Safety Integrity: Designed to meet SIL 3 (Safety Integrity Level 3) requirements, the highest level typically required for industrial safety systems.
        • Nuclear Qualification: Specific versions (e.g., 3721N) are re-qualified and approved by the U.S. Nuclear Regulatory Commission (NRC) for safety-related applications in nuclear facilities.
        • Hot-Spare Capability: Supports "hot-spare" modules, allowing for online, under-power replacement of a faulty module without impacting the running application.
        • Advanced Diagnostics: Continuously monitors hardware health and field-load status, triggering alarms for faults before they lead to system failure.
        • Environmental Resilience: Rated for operation in harsh conditions, with operating temperatures typically ranging from -20°C to +60°C.
        Description
        The Triconex 3721 Analog Input Module is designed for high-reliability, redundant control applications. Each of the three channels asynchronously measures input signals, storing the results in dedicated input tables. These tables are transferred to the associated main processor module and shared across the Tricon system, where the mid-value is selected in TMR mode to ensure accurate, fault-tolerant readings. In duplex mode, the average of inputs is used, allowing flexible configuration depending on system requirements.

        The module supports 32 differential, DC-coupled input points with a 0–5 VDC or ±5 VDC range (±6%). It features 12- or 14-bit programmable resolution, input update rate of 10 ms, and an input resistance of 10 MΩ minimum, while providing current input capability of 0–20 mA with 250 Ω shunt resistor. Overrange protection of 150 VDC / 115 VAC continuous ensures the module withstands industrial electrical transients.

        Each analog input channel is automatically calibrated using multiple reference voltages via an internal multiplexer. The calibration adjusts gain and bias for the ADC, delivering highly accurate readings with <0.15% FSR error from 0° to 60°C. The module also maintains performance in the presence of common mode voltages (−12 V to +12 V peak), with −85 dB common mode rejection and normal mode rejection of −3 dB at 23 Hz, −8 dB at 60 Hz, −14 dB at 120 Hz.

        Designed for a wide range of analog signals, the Triconex 3721 supports not only voltage and current inputs but also thermocouples (K, J, T, E) and RTDs, in both isolated and non-isolated configurations. Status indicators (PASS, FAULT, ACTIVE, FIELD) and a yellow color code allow easy visual verification of module health. This module is ideal for process control systems where reliability, precision, and redundancy are essential.
        Alternative Names
        3008 372I 3625 3624 3604E 3700A 3503E 3703E
        Technical notes
        Built on a TMR architecture, the 3721 ensures that every input is processed through three independent paths and validated via a hardware-voted mid-value selection to eliminate single points of failure. For industrial durability, it offers 800 VDC isolation, 150 VDC over-range protection, and a rapid 10 ms update rate, making it an essential component for high-speed Emergency Shutdown (ESD) and process control systems.
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        FAQS

        The following is a list of questions commonly asked by our customers. Please contact us if you have a question about our process that is not answered below.
        VIEW ALL FAQS
        What voltage input ranges does the 3721 module support?
        0–5 VDC or ±5 VDC (±6%), with optional 0–10 VDC and 4–20 mA support using external wiring.
        How quickly can the 3721 module be shipped?
        Stocked units are typically shipped within 2–3 business days.
        How accurate is the Triconex 3721?
        Accuracy is <0.15% of full scale range (FSR) from 0°C to 60°C.

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