The day-to-day QC reference that catches instrument drift between annual calibrations — how PCS fits in an ISO/IEC 17025 lab’s QC chain, the UCL/LCL framework, and the CS-CINSTAN-PCS specification.
A process control standard (PCS) is a NIST-traceable reference fluid run interleaved through the lab’s normal sample production. Each run’s counts are compared against pre-established upper and lower control limits in the particle-size channels that matter most (typically 4µm, 6µm, and 14µm). PCS data is plotted as a control chart over days, weeks, and months — revealing whether the instrument is producing consistent counts on a known reference or whether it’s drifting in a direction that warrants attention.
PCS is the most operationally important of the three reference-fluid roles in a working lab. Calibration runs once a year. Verification runs occasionally. PCS runs every production batch, often twice (once at the start, once at the end), generating the continuous QC evidence that ISO/IEC 17025 accreditation requires.
The PCS answers a question that calibration and verification can’t address: is the instrument behaving consistently today? Annual calibration sets a point reference. Verification confirms it’s still close. But day-to-day instrument behaviour — gradual sensor fouling, slow channel-table drift, intermittent flow issues — only shows up in the trended control chart. The PCS is what makes that chart.
Three reference materials, three roles, one QC backbone.
| Calibration CINSTAN-CFK |
Verification CINSTAN-VF |
Process Control CINSTAN-PCS |
|
|---|---|---|---|
| Role | Set the channel table | Confirm calibration is valid | Trend day-to-day performance |
| Cadence | Annual | Start of campaign / after change | Every production batch (start & end) |
| Output | New channel-table values | Pass/fail vs certified counts | Control-chart trend over time |
| Annual consumption | 1 kit | 1–4 bottles | Many bottles, depending on batch frequency |
| What if it fails | (N/A — calibration is itself the answer) | Trigger re-calibration | Lock instrument, investigate, re-calibrate if needed |
| ISO 17025 audit value | Annual calibration certificate | Verification record | Continuous QC trend — the most-asked-for audit evidence |
An accredited lab uses all three together, but PCS is the largest line item by volume and the most operationally embedded in daily production. A typical commercial lab running 100–200 samples per day will consume 4–8 PCS bottles per year, depending on the chosen cadence and the lab’s batch structure.
The PCS is only useful if its limits are set correctly. Two questions to answer: where is the centerline, and how wide are the bounds.
Centerline: the certified counts on the PCS Certificate of Analysis. The CINSTAN-PCS CoA gives you the certified particle counts per millilitre at the 4, 6, and 14µm channels. Those numbers are the centerline of the control chart for each channel.
Bounds: standard practice is to set UCL and LCL per the ASTM D7647-10(2018) repeatability statement. The method specifies the maximum allowable variation between replicate measurements on the same sample — that variation, applied symmetrically around the certified counts, defines UCL and LCL for each channel. The method’s repeatability is the loosest acceptable bound; labs may choose tighter bounds (and many ISO/IEC 17025-accredited labs do, especially for stable instruments with strong long-term trend data).
Per-channel limits matter because instrument drift doesn’t affect all channels equally. A sensor fouling at the small-particle end of the size range can shift the 4µm count without measurably affecting 14µm. Setting UCL/LCL independently per channel (4, 6, 14µm at minimum, often plus 21µm for AS4059 reporting) gives the control chart the resolution to spot channel-specific drift early.
CINRG software applies the limits automatically. Sample numbers prefixed (or suffixed) with the configurable PCS marker trigger limit-checking instead of normal sample logic; results are written to a separate PCS output file for trending. If a PCS run falls outside its bounds, the system flags non-conformance and — per the lab’s configured response — either continues the run with the failure logged or halts the batch automatically.
CINRG’s process control standard product is CS-CINSTAN-PCS. Key facts:
CS-CINSTAN-PCS is available through the CINRG online shop or via the CINRG contact form for volume / standing orders, international shipping, or first-time buyers requiring documentation in advance. Standing orders are common for labs running daily production where consistent supply matters.
A process control standard (PCS) is a NIST-traceable reference fluid that’s run repeatedly during normal sample processing and trended against upper/lower control limits to confirm that an optical particle counter is in statistical control. Unlike a calibration fluid (used once a year) or a verification fluid (used at the start of campaigns), a PCS runs interleaved with production samples — typically at the start and end of every batch. It’s the lab’s day-to-day QC backbone.
Three reference materials together build a complete QC chain: annual calibration (sets the channel table), periodic verification (confirms calibration is still good between annual events), and per-batch PCS (catches day-to-day drift). For an ISO/IEC 17025-accredited lab, PCS data is the daily evidence that produces the audit trail — every batch carries traceable proof the instrument was in control when the samples ran.
Standard practice: set UCL and LCL per the ASTM D7647-10(2018) repeatability statement for each of the 4µm, 6µm, and 14µm channels. The certified PCS counts at each channel define the centerline; UCL and LCL bracket that by the method’s repeatability tolerance. CINRG software applies the limits automatically when a sample’s number begins with the configurable PCS prefix. Tighter limits than the method’s defaults are allowed; looser limits are not.
Configurable response. CINRG instruments support two modes: continue the run with the failed PCS flagged in the output file for review, or halt the run automatically to prevent scrap-sample throughput when the instrument has drifted out of control. The right choice depends on the lab’s accreditation requirements and the cost of repouring failed samples. Most ISO 17025-accredited labs configure halt-on-PCS-fail.
CINRG’s recommended cadence is one PCS at the start of every sample batch and one at the end. Some labs add a mid-batch PCS for runs over 50 samples, or run a PCS automatically after every N samples by suffixing those samples with the PCS prefix in the batch file. Higher cadence catches drift earlier at the cost of higher PCS consumption.
PCS is run frequently (every batch) at lower per-bottle cost; VF is run occasionally (start of campaign) and answers a different question. PCS is the daily/per-batch QC; VF is the calibration-still-valid check. Both are traceable to NIST SRM 2806d but serve different roles in the lab’s QC chain.
4 × 400 mL bottles, NIST SRM 2806d-traceable, in ISO 40 API Group II white oil. Standing orders available for daily-production labs.
Tell us about your throughput, your test methods, and your facility. A CINRG engineer will help you scope the right configuration — and put you in touch with your nearest dealer.