The Q64RDN is Mitsubishi Electric’s 4-channel high-accuracy resistance thermometer input module for the MELSEC-Q programmable controller series, providing precision temperature measurement from Pt100, Pt1000, and JPt100 RTD sensors for data acquisition, monitoring, and process feedback applications where temperature measurement accuracy and resolution are the primary requirements — without the integrated PID control output of the Q64TCRTBWN, making it the correct choice for applications where temperature data is used by the CPU program for custom control logic, data logging, or multi-variable process calculations rather than direct PID output generation. Atlantech Drives holds stock of the Q64RDN. Contact us for fast worldwide delivery and competitive pricing.
What Is the Q64RDN?
The Q64RDN is a MELSEC-Q series intelligent function module providing four channels of high-accuracy RTD temperature measurement. Unlike the Q64TCRTBWN temperature control module, the Q64RDN is a pure measurement module — it reads RTD sensor values and makes the measured temperatures available in its buffer memory for the CPU program to read via FROM instructions or GX Works2 auto-refresh, but does not generate any analogue output signal or execute PID calculations internally. This measurement-only architecture makes the Q64RDN the appropriate choice for applications where temperature data feeds into custom CPU-based control algorithms (such as cascade control, feedforward compensation, or multi-variable MPC strategies), for quality monitoring systems recording temperature profiles during product manufacturing, and for condition monitoring applications tracking equipment temperatures for predictive maintenance purposes. The Q64RDN supports 3-wire RTD connections with built-in lead resistance compensation, maintaining measurement accuracy across the full cable length between the RTD sensor and the module.
Key Technical Specifications
- Model: Q64RDN
- Input Channels: 4
- Module Type: RTD input measurement only (no analogue output)
- Input Type: Pt100 (3-wire), Pt1000 (3-wire), JPt100 (3-wire)
- Temperature Range: -200°C to +850°C (Pt100/JPt100); -200°C to +850°C (Pt1000)
- Input Resolution: 0.1°C
- Input Accuracy: ±0.3°C at 25°C ambient (±0.8°C over full operating temperature range)
- Lead Resistance Compensation: Built-in 3-wire compensation
- Conversion Speed: 40 ms per channel (all 4 channels updated every 160 ms)
- Isolation: Optical, each channel independently isolated from internal bus
- Current Consumption (5 VDC internal bus): 0.35 A
- External Power Supply: 24 VDC ±10%, 0.20 A (required)
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.22 kg
Typical Industrial Applications
The Q64RDN is widely deployed in quality assurance and process monitoring applications where temperature measurement data drives CPU-based decision logic rather than direct analogue output control. In pharmaceutical tablet coating processes, the Q64RDN monitors inlet air temperature, outlet air temperature, product bed temperature, and exhaust temperature simultaneously — the CPU compares these four values to a validated temperature profile and adjusts spray rate, drum speed, and airflow setpoints via separate analogue output modules, implementing a multi-variable control strategy that would not be possible with a standalone temperature controller. In steel and aluminium heat treatment furnaces, the Q64RDN provides the temperature feedback for custom CPU-based temperature ramp-and-soak programs, where the heating profile (ramp rate, soak time, cooling rate) varies by product batch and is selected by the operator via the HMI — the flexibility of CPU-based control allows the temperature profile to be modified without changing module parameters. Condition monitoring systems for large electric motors and transformers use the Q64RDN to track winding and bearing temperatures via embedded Pt100 sensors, with the CPU implementing thermal model calculations that predict remaining insulation life based on cumulative thermal stress — a more sophisticated approach than simple over-temperature alarms. In food and beverage pasteurisation systems, the Q64RDN provides the temperature measurement for HACCP critical control point monitoring, with the CPU logging measured temperatures to non-volatile storage via an SD memory card module for regulatory compliance documentation.
Troubleshooting Guide
If the Q64RDN reports an abnormal temperature reading on one or more channels, the diagnostic sequence should begin with the module’s error code registers in buffer memory, accessible via GX Works2’s buffer memory monitor. Error code 0x0400 (input disconnection) indicates that the RTD circuit is open — check the RTD sensor continuity and terminal connection for the affected channel. Error code 0x0800 (input short circuit) indicates a resistance below the valid RTD range — check for wiring shorts between the RTD leads or a damaged sensor element. If no error code is present but the temperature reading is offset from the expected value, the most likely cause is lead resistance imbalance between the three RTD conductors — measure each conductor’s resistance individually and verify they are within 0.1 Ω of each other. For readings that fluctuate erratically without sensor or wiring faults, check the grounding of the module’s external 24 VDC supply — a poorly grounded supply with high common-mode noise can couple into the RTD measurement circuit and cause reading instability. Ensure the 24 VDC supply’s negative terminal is connected to the panel protective earth at a single point, and that the RTD cable shield is earthed at the module end only (single-point earthing) to prevent earth loop currents from degrading measurement accuracy.
Frequently Asked Questions
Q: What is the difference between the Q64RDN and the Q68RD3-G, and when should each be specified?
A: The Q64RDN provides four RTD input channels with 0.1°C resolution and ±0.3°C accuracy, while the Q68RD3-G provides eight channels with higher resolution (0.01°C) and improved accuracy for applications requiring sub-degree precision across more measurement points. Specify the Q64RDN for standard industrial temperature monitoring with four zones; specify the Q68RD3-G for high-channel-count precision measurement where per-channel accuracy better than ±0.3°C is required. For applications requiring fewer than four channels, the Q64RDN is more economical than the Q68RD3-G regardless of accuracy requirements.
Q: Can the Q64RDN detect RTD sensor disconnection automatically and trigger a CPU alarm?
A: Yes. The Q64RDN monitors each channel for open-circuit RTD conditions and sets a corresponding disconnection detection bit in the buffer memory when a disconnection is detected. The CPU ladder program can monitor this bit using an auto-refresh mapping in GX Works2 and trigger an alarm output, HMI message, or safe-shutdown sequence automatically. The disconnection detection response time is within two conversion cycles (320 ms maximum) of the fault occurring.
Q: Does the Q64RDN support 4-wire RTD connections for higher accuracy?
A: No. The Q64RDN supports 3-wire RTD connections only. Four-wire RTD connections, which provide the highest possible lead resistance compensation accuracy, are not supported by the Q64RDN’s input circuit. For applications requiring 4-wire RTD accuracy, external signal conditioning transmitters (converting 4-wire RTD to 4–20 mA) can be used to feed the Q64AD analogue input module, achieving equivalent accuracy through an alternative signal path.
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