The Q64RD is a 4-channel resistance temperature detector (RTD) input module from Mitsubishi Electric for the MELSEC-Q series, enabling direct connection of Pt100, Pt1000, Ni100, and other RTD sensor types for precision temperature measurement in industrial process control applications. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the Mitsubishi Q64RD?
The Q64RD is an intelligent function module that provides 4 independent RTD input channels, each configurable for different sensor types and measurement ranges directly via GX Works2 parameters — no ladder logic is required for channel configuration or scaling. The module performs 3-wire or 4-wire RTD measurement to compensate for lead wire resistance, ensuring measurement accuracy is maintained even with long sensor cable runs. Converted temperature values are written to the module’s buffer memory and can be read by the CPU via auto-refresh assignment or FROM instructions, and alarm outputs (upper/lower limit) are available per channel for integration into PLC control logic without additional software computation.
Key Technical Specifications
- Number of input channels: 4
- Supported RTD types: Pt100, Pt1000, JPt100, Ni100, Ni1000, Cu10, Cu50
- Measurement range (Pt100): –200 to +850°C
- Resolution: 0.1°C (digital output in units of 0.1°C)
- Overall accuracy: ±0.5°C (Pt100, at 25°C ambient)
- Wiring method: 3-wire or 4-wire RTD connection
- Conversion speed: 40 ms per channel (all 4 channels: 160 ms total)
- Isolation: Optical isolation between channels and internal bus
- Alarm function: Upper/lower limit alarm per channel, with hysteresis setting
- Disconnection detection: Yes (per channel, with CPU error flag)
- Number of occupied I/O points: 16
- Power consumption: 5 V DC, 0.30 A (internal bus)
- Operating temperature: 0 to 55°C
Series Comparison & Selection Guide
Within the MELSEC-Q temperature input module range, the Q64RD is the standard RTD module. Key distinctions for selection:
- Q64RD vs Q64RD-G: The Q64RD-G adds a disconnection detection function with enhanced diagnostics and supports a wider range of RTD types including Cu10 and Cu50 copper RTDs. If copper RTD sensors are used in the application, the Q64RD-G is the required selection.
- Q64RD vs Q64TD: The Q64TD is a thermocouple input module (K, J, T, B, S, R, E, N, U, L types), not an RTD module. RTDs (Pt100, Ni100) offer higher accuracy and better long-term stability than thermocouples at the cost of slower response and higher sensor cost — choose RTD for precision process temperature control and thermocouples for high-temperature or fast-response applications.
- Q64RD vs R60RD4: The R60RD4 is the iQ-R series equivalent module for newer MELSEC iQ-R CPU systems. The Q64RD is designed exclusively for MELSEC-Q CPUs and is not compatible with iQ-R bases.
Maintenance Tips
- Periodically verify RTD sensor accuracy by comparing Q64RD readings against a calibrated reference thermometer at a known stable temperature point. RTD elements can drift over time due to mechanical stress on the sensor element, particularly in high-vibration environments — an annual calibration check is recommended for critical process temperature loops.
- Inspect RTD cable terminations at the Q64RD terminal block annually for signs of oxidation or loose connections. A high-resistance connection in a 3-wire RTD circuit introduces a systematic positive temperature error that increases progressively as the connection degrades — this is frequently misdiagnosed as sensor drift rather than a wiring fault.
- If a channel shows a disconnection alarm (D.ALM flag set in buffer memory), check the RTD sensor wiring continuity before replacing the module. Disconnection detection is highly reliable on the Q64RD and almost always indicates a genuine open circuit in the sensor or cable, not a module fault.
- When replacing a Q64RD in a running system, note that all channel parameters (RTD type, range, alarm settings, averaging) are stored in the CPU parameter file via GX Works2 auto-refresh settings and will be automatically downloaded to the replacement module on the next CPU power cycle — no manual re-parameterisation is required if GX Works2 parameters are correctly backed up.
Frequently Asked Questions
Q: Can Pt1000 sensors be connected to the Q64RD using the same wiring as Pt100?
A: Yes, mechanically the wiring is identical — both use 3-wire or 4-wire RTD connection to the same terminal block. However, the channel RTD type parameter in GX Works2 must be changed from Pt100 to Pt1000, as the module uses different resistance-to-temperature conversion coefficients for each sensor type. Mixing up the parameter setting is a common commissioning error that results in grossly incorrect temperature readings.
Q: What is the maximum cable length between the RTD sensor and the Q64RD?
A: For 3-wire connection, the maximum recommended cable length is 200 m using 0.5 mm² conductors. For 4-wire connection, cable length has less impact on accuracy as lead wire resistance is fully compensated. Use shielded cable for all RTD sensor connections and connect the shield to earth at the Q64RD end only.
Q: Is the Q64RD compatible with 2-wire RTD sensors?
A: The Q64RD supports 3-wire and 4-wire RTD connection only. 2-wire RTD connection is not supported because without a separate lead wire compensation path, the module cannot distinguish sensor resistance from cable resistance, making accurate temperature measurement impossible for any cable run of practical length.
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