How the Spirometer's Daily Calibration and 3-Liter Syringe Check Works

What's happening

Spirometers are checked daily with a hand-operated 3-liter calibration syringe, and this comes up often enough as an audit question that it's worth explaining plainly. The syringe and the spirometer are checked together — the syringe isn't a separate certified instrument that gets checked once and trusted forever, and it isn't calibrated apart from the spirometer it's plugged into.

The CCS-200's daily calibration is three specific flow tests, run in order: a High Flow test, a Mid Flow test, and a Low Flow test. For each one, you pull the syringe plunger all the way out, pause at least 3 seconds, then push it back in smoothly over the time the software specifies for that step on screen — the Mid Flow push takes 3 seconds and the Low Flow push takes 6 seconds; High Flow is the fastest of the three and the software displays the exact pace to follow at that step. That confirms the spirometer measures volume accurately across the range of flows a real forced exhalation produces, not just at one speed. The CCS-200 displays the resulting volumes both graphically and numerically directly on the printout — the numbers aren't retyped onto a separate calibration log, which avoids a transcription error creeping into the record. The calibration certificate generated from that printout is the record for that day's spirometer-and-syringe pair.

The daily calibration is a different, shorter procedure from the CCS-200's separate Linearity Check feature. A linearity check repeats each of the three flow rates three times (nine strokes total) instead of once, doesn't update the day's calibration correction factor, and per the 2005 ATS/ERS standard is meant to be run about once a week rather than daily. If your software prompts you toward a linearity check specifically, that's the weekly test, not the daily one — don't substitute one for the other.

The daily calibration has a built-in accuracy tolerance, not a single fixed target. The spirometer's allowed deviation and the syringe's allowed deviation are set separately, then added together to get the total window the volume reading is allowed to fall within, measured against the 3-liter syringe. On the standard "2019 ATS/ERS 3-Liter Syringe" configuration, that's 2.5% for the spirometer plus 0.5% for the syringe — 3% of 3 liters, or 90 mL, meaning a passing reading has to land between 2.91 and 3.09 liters. Other configurations (2005 ATS/ERS, OSHA Cotton Dust, SSA/DDS) use different percentages; check which configuration is selected under Daily Calibration > Configuration in the Spirometer menu if you need the exact number for your setup.

Try these in order

The software reports a specific reason for each failed attempt in the Guidance window, and it's worth reading that message before troubleshooting anything else — every one of these messages describes a technique problem, not a spirometer fault:

1. "No flow detected" means the pause between drawing the plunger out and pushing it in was too short. Draw the plunger all the way out, pause at least 3 full seconds, then push.
2. "Syringe discharge is too slow" or "too fast" means the push didn't match the pace line the software shows on screen for that step (a 3-second push for Mid Flow, 6 seconds for Low Flow, and a faster pace shown on screen for High Flow). Watch the red pace line during the push, not just the plunger.
3. "Volume is too low" means the plunger wasn't drawn all the way out or pushed all the way in — check for a hard stop at both ends of the stroke. "Volume is too high" means the plunger is slamming into the end of the syringe on the push; ease off just before it bottoms out.
4. Confirm the syringe is fully seated on the connection to the spirometer if none of the above messages match what you're seeing, or if the reading is consistently off by roughly the same amount at every flow rate — a loose or partially seated connection behaves like a leak, not like a technique error, and won't match any of the specific messages above.

If it still won't pass

If you've worked through the specific failure message shown, confirmed the connection is fully seated, and a careful re-attempt at all three flow rates still won't land in range, stop testing on that unit and contact us. Continuing to test with a unit that's failing its own daily calibration puts every result recorded that day in question.

When to call us

• The daily calibration consistently fails at all three flow rates after you've ruled out pause timing, push pace, plunger travel, and a loose connection.
• One specific flow rate (High, Mid, or Low) keeps failing on repeated, correctly-paced attempts while the other two pass.
• An auditor is asking for documentation beyond the printed calibration certificate.

You can reach us at (513) 891-0868 or service@fosterinstruments.com.