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Turbidity calibration

Two-point calibration with the 1 L tube and PEBL 10 mL formazin standard.

tip

This is the precise bench procedure. Do it as part of Connect and configure, straight after calibrating the heading (compass).

You will need​

  • GrowProbe with calibration collar and 1 L perspex tube
  • Phone with the GrowProbe app, paired to the probe
  • One 10 mL PEBL formazin standard bottle
  • About 1.5 L of cold tap water, drawn 1 to 2 minutes before use
  • Marigold-style rubber gloves and kitchen paper
  • A clean stirring utensil (chopstick, teaspoon handle)

1. Set up the probe and start calibration​

  • Wipe the optical window with clean kitchen paper. Fit the rubber collar.
  • Slide the 1 L perspex tube onto the collar and stand the probe upright.
  • Open the GrowProbe app, connect to the probe, and tap Calibrate.

2. Zero point: tap water​

info

In the app, enter 0.5 NTU.

  • Pour cold tap water slowly down the side of the tube to the 1 L mark.
  • Tap the tube once or twice to dislodge any bubbles on the lens.
  • Wait 30 seconds, then press OK.

3. Span point: 40 NTU standard​

info

In the app, enter 40 NTU.

  • Pour about 500 mL of tap water into the tube first.
  • Empty one 10 mL formazin bottle into the tube.
  • Rinse the empty bottle twice with tap water and pour each rinse into the tube. This captures any residual standard.
  • Top up with tap water to the 1 L mark.
  • Stir gently for 10 to 15 seconds with a clean kitchen utensil. Do not shake.
  • Wait 60 seconds, then press OK.

4. Finish and clean up​

  • Calibrating multiple probes the same day: reuse the 1 L of 40 NTU standard. Keep the tube covered, and discard after 24 hours.
  • When done, drain to a foul-water (sewer) drain with running water. Not to surface drains.
  • Rinse the optical window, the tube and the collar with clean tap water.
  • Wash the stirring utensil with hot soapy water before returning it to the kitchen. Do not reuse for food without washing.
  • Recycle the empty 10 mL bottle. Once opened, the standard cannot be reused.

When to calibrate​

Pre-deployment. Run the full 2-point calibration each time before the probe goes in the water.

Post-recovery. Read 40 NTU with the window dirty, then clean it and read again. The dirty reading corrects for fouling; the clean reading shows sensor drift. Use a fresh 10 mL bottle.

Safety​

warning

Wear rubber gloves (Marigold-style is fine). Avoid skin contact and breathing in spray. PEBL formazin 4000 NTU is Skin Sens. 1 (H317, signal word Warning).

If it gets on skin, wash with soap and plenty of water. If irritation persists, get medical advice.

Full Safety Data Sheet (16 sections), printed copy free on request: pdf.dutscher.com/doc/775322/775322_FDSen.pdf

Need help?​

Get in touch at hello@pebl-cic.co.uk or +44 7905 672766.