MAINTENANCE & CALIBRATION PROCEDURE: TURBIDIMETERS

These procedures are to be performed by Streamkeeper staff. Calibrate the turbidimeters before at least every other monitoring session. Replace primary and secondary (sealed) reference standards as needed so as not to exceed expiration dates. Solutions are good until the last day of the month listed on the expiration date.

EQUIPMENT NEEDED:

· “Maintenance & Calibration” notebook

· HF Scientific Turbidimeters, models DRT-15C and DRT-15CE—these should be fully charged before calibrating

· Sealed secondary field standards—each meter should have a “low” vial in the .02 NTU range and a “high” vial in the 8-10 NTU range

· Calibration instructions for both models (in “Maintenance & Calibration” binder).

· Kimwipes & glass cleaner from field kit

· Blue plastic “Turbidimeter Reference Standards” box containing vials marked for different turbidity solutions. These vials should already have index arrows on their caps—if they do not, you will have to index them using the instructions below. After removing any cap, be sure to replace it on the same vial!

· Polymer standard solutions, or…

· If you are using Formazin to make calibration standards, you will need to use the Environmental Health Lab (arrange for some counter space for ½ day) and:

· safety goggles

· latex gloves

· turbidity free water

· pipettes of different sizes from card-board “Turbidimeter Standards” box

· volumetric flasks and pipette suction bulbs from the Env. Health Lab

CALIBRATION PROCEDURE:

1) Warm up turbidimeters for 15 minutes before calibrating.

2) If you are using Formazin, prepare calibration solutions, using the Formazin dilution chart on p. 4 of the instruction manual:

a) Put the suction bulb on the appropriate pipette.

b) Use the pipette to measure Formazin into the appropriate volumetric flask (or 400-ml beaker).

c) Fill the rest of the flask with turbidity-free water, to the volume stated on the chart.

d) Swirl the solution and label the flask.

3) Open the blue plastic box labeled “Reference Standards.” Pour out the liquid in each labeled vial, capping each vial immediately after emptying it.

4) For each labeled vial:

a) Fill ¼ full with the appropriate strength solution, recap, agitate, and discard.

b) Refill and recap with the appropriate strength solution.

5) If you are using Polymer standard solutions, the bottle labeled “0.0 NTU” is actually 0.02 NTU; you’ll need to know this for calibration.

6) Any vial you’ll be using should have a piece of tape on top with an arrow. If it doesn’t, you’ll have to index the vial. This is a process whereby you mark the orientation of the vial that yields the best light transmission through the meter:

a) A vial can only be indexed to a single meter.

b) Set the meter to the appropriate range for the contents of the vial.

c) Put the vial into the well.

d) Note the meter reading.

e) Make a small pencil mark on the cap at the point nearest to the white locator pin on the rim of the well.

f) Slowly rotate the vial while observing the meter reading, and make a new mark every time you get to a new lowest reading. When you arrive back at your first mark, it’s a good idea to go back around backwards, to recheck the lowest-reading point. Once you have confirmed that point, put a piece of tape on the cap with a small arrow pointing to that point.

7) When all of the vials have been prepared, calibrate each turbidimeter individually, following instructions for that model. (For the DRT-15CE, they are available on the Web at http://www.hfscientific.com/PDF%20-%20Manuals/DRT-15ce/Manual%20DRT-15ce.pdf.)

8) Once the machine has been calibrated, clean the sealed secondary “low” and “high” reference vials and take readings for them; the company guarantees that they will read within 20% of their listed value. (If they don’t, contact the company.) On a piece of tape on the cap that includes a properly-oriented index arrow, write “Ref. Std. [reading on meter] NTU / DO NOT OPEN!” Record these readings for the secondary standards in the calibration notebook.

9) Put a new label on the control panel of the turbidimeter, reading “Last Calibration [date][initials].”

10) After calibrating:

a) If you are using Formazin:

i) Pour the Formazin into the sink.

ii) Rinse vials, flasks, and pipettes with tap water, then distilled water.

iii) Fill vials with distilled water, cap, and store.

b) If you are using polymer solutions, leave these solutions in the vials to store them.

MAINTENANCE & CALIBRATION NOTEBOOK:

Record all calibration and maintenance activity in the “Streamkeepers Maintenance & Calibration” binder kept in the Streamkeepers office. In the case of calibration, record the type of calibration solution, vendor, expiration date, and readings on the secondary field standards. This provides confirmation that the secondary field standards were checked.

CALIBRATION TROUBLESHOOTING:

If you are having trouble calibrating the instrument, you may have one of the following problems:

• Battery needs charging or replacing.
• Photo diodes may be loose. Check leads to circuit board from detectors in optical block, by plucking gently.
• Lamp may need replacing, particularly if you are having trouble calibrating at the high end.