Q68ADVN is an 8-channel analogue voltage input module for Mitsubishi Electric’s MELSEC-Q series programmable logic controller platform, providing 16-bit resolution conversion of voltage signals in the ±10 V DC, 0–10 V DC, or 0–5 V DC input ranges for precision process measurement and control applications. The Q68ADVN integrates conversion averaging, scaling, and alert output functions directly in the module hardware, offloading signal conditioning tasks from the CPU scan cycle and delivering stable, high-resolution process values to the Q-series data registers at conversion speeds of 80 µs per channel. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the Q68ADVN?
The Q68ADVN is an intelligent analogue input module that occupies a single slot on any Q-series main or extension base unit. The «68» in the part number indicates 8 analogue input channels, «AD» identifies the module as an analogue-to-digital converter, «V» specifies voltage input only (as opposed to the Q68ADI for current input or Q68ADV for combined voltage/current), and «N» denotes the normal resolution variant with the standard 16-bit conversion architecture. All 8 channels convert simultaneously — or can be configured for sequential conversion to trade channel count for faster individual channel update rates — and each channel is individually configurable for input range, averaging method, and alarm thresholds independently of the other channels. The module communicates with the Q-series CPU via the intelligent function module buffer memory, accessed using FROM/TO instructions in the ladder program or via direct device mapping in GX Works2 auto-refresh parameter settings, which copies buffer memory values to data registers (D devices) automatically at each CPU scan without explicit FROM instructions in the program.
Key Technical Specifications
- Number of Input Channels: 8 (voltage input only)
- Input Voltage Ranges: ±10 V DC, 0–10 V DC, 0–5 V DC (per channel, selectable)
- Resolution: 16-bit (1/64,000 of full scale)
- Conversion Speed: 80 µs per channel (all 8 channels: 640 µs total)
- Accuracy (at 25 °C): ±0.1% of full scale (±10 V range)
- Temperature Drift: ±0.01%/°C of full scale
- Input Impedance: 1 MΩ (voltage input)
- Averaging: Sampling count (2–4096 samples), time average (2–5000 ms), or moving average
- Alert Output: Upper/lower limit alert per channel (flag in buffer memory)
- Isolation: Between channels and Q-bus (transformer isolation); not isolated channel-to-channel
- External Power Supply: Not required (powered from Q-bus 5 V DC)
- Current Consumption: 5 V DC, 0.56 A (from Q-bus)
- Operating Temperature: 0 °C to 55 °C
- Dimensions (W × H × D): 27.4 × 98 × 90 mm
- Weight: Approx. 160 g
Architecture & Design Overview
The Q68ADVN implements a successive approximation register (SAR) ADC architecture with 16-bit resolution per channel, providing a digital output range of 0–64,000 counts for unipolar input ranges and -32,000 to +32,000 counts for the ±10 V bipolar range. This digital output scaling is directly compatible with Mitsubishi’s standard analogue scaling convention used across the Q-series analogue module family, simplifying the engineering of normalisation routines when multiple analogue module types are used in the same system. The module’s internal microprocessor handles conversion sequencing, averaging computation, and alert flag generation independently of the Q-series CPU, meaning that averaging over 4,096 samples or a 5,000 ms time window does not introduce any latency or processing overhead into the CPU scan cycle. The auto-refresh function, configured in GX Works2’s intelligent function module parameters, allows the module to copy its 8 channel digital output values to consecutive data registers (e.g., D100–D107) automatically at every CPU scan end, without any FROM instruction in the ladder program — this is the recommended configuration for continuous process monitoring applications as it minimises program complexity and ensures consistent data refresh timing. For applications requiring sample-synchronous data capture (such as vibration analysis or rapid process disturbance detection), the Q68ADVN supports an interrupt-driven read mode where the module triggers a CPU interrupt on completion of each conversion cycle, allowing the ladder program to capture instantaneous channel values at precisely controlled intervals independent of the normal scan timing.
Expert Tips
When wiring voltage inputs to the Q68ADVN, use individually shielded twisted-pair cable for each channel, with the shield grounded at the module end only — grounding both ends creates a ground loop that introduces 50/60 Hz common-mode noise directly onto the signal. For transmitters with a 4–20 mA current output (rather than voltage), do not use the Q68ADVN — specify the Q68ADI (current input) or Q64AD (combined 4-channel voltage/current) instead; connecting a current-loop transmitter to the Q68ADVN voltage input will damage the module’s input circuit due to the low 1 MΩ input impedance presenting near-zero voltage drop across the current loop. When configuring averaging, use time averaging rather than sampling count averaging for slowly varying process signals (temperature, pressure) — time averaging produces more stable readings at the cost of a longer settling time after a step change, while sampling count averaging responds faster but may show more noise on slow-moving signals. If unused input channels are present, configure them as «unused» in the GX Works2 module parameter rather than leaving them active with floating inputs — an active channel with no connected signal will produce a fluctuating digital output value that consumes buffer memory bandwidth and may trigger spurious alert outputs. For high-accuracy applications near the ±0.1% specification limit, allow the module to warm up for 30 minutes after power-on before relying on calibrated readings, as the internal reference voltage stabilises during this period.
Frequently Asked Questions
Q: Can the Q68ADVN measure differential (floating) voltage signals, or only single-ended signals referenced to a common ground?
A: The Q68ADVN inputs are single-ended — each channel has a V+ input terminal and a shared COM terminal. For differential voltage sources (such as thermocouple amplifiers or isolated transmitters with floating outputs), connect the signal positive to V+ and the signal negative to COM, ensuring the floating source’s common-mode voltage relative to the PLC ground does not exceed the module’s common-mode rejection specification. For true differential measurement with high common-mode voltage, a dedicated differential input module or signal conditioning isolator is required.
Q: What is the maximum cable length for analogue signal wiring to the Q68ADVN?
A: Mitsubishi does not specify a hard maximum cable length for the Q68ADVN, as acceptable length depends on the source impedance of the transmitter, the cable capacitance per metre, and the ambient electromagnetic noise level. As a practical guideline, shielded instrumentation cable runs up to 200 m are routinely used with low-impedance voltage transmitters in low-noise industrial environments without measurable accuracy degradation. For longer runs or noisy environments, use a 4–20 mA current loop transmitter with the Q68ADI module instead, as current loops are inherently immune to resistive voltage drop over long cable runs.
Q: Is the Q68ADVN compatible with iQ-R series base units?
A: No. The Q68ADVN is mechanically and electrically specific to the MELSEC-Q base unit form factor and Q-bus interface. Mitsubishi’s iQ-R series uses the R-bus architecture with a different connector and communication protocol. The functional equivalent for iQ-R systems is the R60AD8-G (8-channel voltage/current input, 16-bit) or R60ADV8 modules.
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