CLX DPD accuracy: turn a datasheet tolerance into an acceptance requirement

Updated

A CLX acceptance requirement should state the model, operating range, reference method and applicable tolerance. Resolution, accuracy and biological ballast-water compliance are different measures.

Current-generation HF scientific CLX analyser, manufacturer illustration from its operating manual
Current-generation HF scientific CLX analyser, manufacturer illustration from its operating manual. Credit: HF scientific, a Watts brand. Illustrative model, not a compatibility confirmation for every installation.

Key takeaways

  • State model, range and applicable accuracy.
  • Define sampling and reference method.
  • Keep resolution, calibration and biological compliance separate.

Understand what the analyser measures

The XT manual describes DPD colorimetry using a 515 nm LED: reagent produces colour in response to oxidants, and the instrument compares the reacted sample with the unreacted sample. In a BWMS application this supports TRO monitoring. It does not directly count organisms, and a satisfactory TRO reading does not by itself demonstrate biological D-2 compliance.

Apply the larger term in the accuracy statement

For the supplied XT standard range through 6.0 mg/L, the stated tolerance is ±5% of reading or ±0.03 mg/L, whichever is greater. At 0.20 mg/L, 5% is 0.01 mg/L, so the 0.03 mg/L term governs. At 4.0 mg/L, 5% is 0.20 mg/L and governs instead. These are illustrations of the stated specification, not a complete measurement-uncertainty budget.

Avoid using display digits as acceptance evidence

A fine display resolution does not prove equally fine accuracy. The reference method has its own uncertainty, sampling can introduce differences, and changing concentrations can make non-simultaneous samples incomparable. Specify the sampling arrangement and time relationship, reference equipment and applicable procedure. Do not invent an arbitrary agreement percentage that conflicts with the monitor's specified performance.

Define certificate scope before service

An RFQ for calibration should identify the instrument and range, required reference, acceptance basis and report contents. Clarify whether the work includes adjustment, verification before and after service, or only a documented check. Sea Clean can scope instrument service and calibration; it is not an accredited laboratory, and a calibration document must not be represented as BWMS type approval or a biological test result.

Illustrative procurement scenario

A purchaser expects every reading to agree within 5%, including very low concentrations. The specification review identifies the absolute ±0.03 mg/L term and establishes a realistic, documented acceptance method before attendance.

Request a matched CLX quotation

Sea Clean is a Watts distributor. We source, supply and repair all CLX variants and supply normal, zig-zag and J.A.W. TRO reagent kits competitively. Stocked products are ready for delivery; confirm the exact item and quantity. Estimated DHL Express transit is 1–4 days on suitable routes, subject to dispatch, customs and final vessel handover.

For this enquiry, include: Monitor model/serial; range; required calibration or verification; reference method; acceptance criteria; certificate requirements; port and date.

Equipment enquiries: CLX monitor supply

Consumables: TRO reagent kits

Service support: BWTS service and calibration

Frequently asked questions

Is a 0.001 mg/L display resolution the same as ±0.001 mg/L accuracy?

No. Display resolution is the smallest displayed increment; use the manufacturer's accuracy specification and a suitable verification method.

Manufacturer PDFs & direct enquiries

Original manufacturer documents hosted directly by Sea Clean. Match the model and revision before use.

Email CLX enquiry to post@seaclean.no

Opens an email draft. Attach nameplate and bottle photographs, add your requirements, then send. No website form.

Explore all 15 CLX buying and service guides

Sources

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