Nephelometer Zero & Span Calibration

 

Purpose:  Follow these steps to Zero and Span calibrations of the Nephelometer instrument.

 

Required Equipment:  Nephelometer Calibration Kit

Pure CO2 to use for span gas

Psychrometer

 

Reference:  SOPMAN

 

 

Notes:  Calibration is accomplished by filling the instrument with gases of known but different scattering coefficients and adjusting the zero and span constants for the appropriate scattering values (bs or bscat) on either the display screen or analog output.  Particle free air is used as a zero reference scatter and one of several gases can be used as an upscale scatter.  Pure CO2 will be introduced in this procedure to be the span reference.

 

 

Procedure Time:  Calibration time depends upon the signal averaging time selected since that is the time required for the output to stabilize.  However, pressing the reset switch to average periodically will decrease the stabilization time.  The procedure should take only 20 to 30 minutes.  The instrument will have to be removed from sample plumbing and set on workbench to carry out procedures.  Vibration will effect this instrument so be sure you do not bump or have it setting on a vibrating surface.

 

 

 

Procedures:

 

Zero Calibration: Bench Top Method

  1. Start by filling out the calibration form up to the Nephelometer Zero Cal section.
  2. Down the Aethalometer & Nephelometer channels before starting any manual calibration.
  3. Disconnect the instrument and set up on a bench top work area.
  4. Vibration will effect this instrument so be sure you do not bump or have it setting on a vibrating surface.  Picture of this setup can be found in figure #1 below.
  5. Turn power on to the instrument.
  6. Thread the two PVC adapter fittings from calibration kit into the inlet and outlet ports.
  7. Connect the zero filter assembly on the top inlet port.
  8. Connect PVC fitting with the box fan bolted onto the lower outlet port.
  9. Plug white electrical plug from fan into connector supplied on back of control box.
  10. Allow fan to run for ten minutes before taking readings.
  11. Press the Next toggle switch three times and read the Wall % number on the instrument display.  Enter this into the calibration form.  If the Wall % number is greater than 75% contact the Plano office.
  12. Use the Display toggle switch to obtain the Zero Calibration Screen as shown in picture below.

  1. Read the bscat number.  This number should be 0.00 to + 0.05e-5.  If this number is between the specifications your Zero is good.  Set the Neph channel to DAP Integer and obtain the number corresponding to the specification and add this to the DAP integer line of the form.   Continue to the Span calibration portion of this procedure.
  2. If this number is not within specification continue on with this calibration portion of the procedure.
  3. In the lower right hand corner of the display there is a Set Zero number.  Write it down in the Set Zero as found line of the calibration form.  Use the Parameter toggle switch to adjust this number to be less or more.  As this parameter number changes watch the bscat to obtain the specification listed earlier.  You will find that as you make an adjustment you must wait for the bscat data to settle down.  Use one minute intervals to fill in the value portions of the calibration form. Once you have reached 0.00 to +0.05e-5 the Zero calibration is complete.
  4. Write into the calibration form the final Set Zero after parameter number.  Set the Neph channel to DAP Integer and obtain the number corresponding to the specification and add this to the DAP integer line of the form.
  5. Continue to the Span calibration portion of this procedure.

 

Zero Calibration: Inlet Connected / Ball Valve Method

  1. Start by filling out the calibration form to the Nephelometer Zero Cal section.
  2. Vibration will affect this instrument so be sure to limit vibration and or bumping it while calibration is happening.
  3. Down the Aethalometer & Nephelometer channels before starting any manual calibration.
  4. Select SO2 Zero from the DAS to switch the ball valve on the Aeth/ Neph zeroing box.  This switch bypasses the inlet air through a filter to simulate a zero particle stream.  Allow the SO2 Zero to run for ten minutes before taking readings from the Nephelometer display.
  5. Under Display press the Next toggle switch three times and read the Wall % number on the instrument display.  Enter this into the calibration form.  If the Wall % number is greater than 75% contact the Plano office.
  6. Use the Display toggle switch to obtain the Zero Calibration Screen as shown in picture below.

  1. Read the bscat number.  This number should be 0.00 to + 0.05e-5.

If this number is between the specifications your Zero is good.  Set the NEPH channel to DAP Integer and obtain the number corresponding to the specification and add this to the DAP integer line of the form.  Continue to span calibration portion of this procedure.

If this number is not within specification continue on with this calibration portion of the procedure.

  1. In the lower right hand corner of the display there is a Set Zero parameter number.  Write it down in the Set Zero as found line of the calibration form.
  2. Use the parameter toggle switch to adjust this number to be less or more.  As this parameter number changes watch the bscat to obtain the specification listed earlier.  You will find that as you make an adjustment you must wait for the bscat data to settle down.  Use one minute intervals to fill in the value portions of the calibration form.  Once you have reached 0.00 to +0.05e-5 the Zero calibration is complete.
  3. Write into the calibration form the final Set Zero after parameter number.  Set the Neph channel to DAP Integer and obtain the number corresponding to the specification and add this to the DAP integer line of the form.
  4. Continue to the Span calibration portion of this procedure.

Figure 1:  Setup for Zero Calibration Bench Top Method

 

 

 

 

Span Calibration: Bench Top Method

  1. Pictures of this setup are shown below in figures 2 & 3.
  2. Remove the zero filter assembly from the top port if following the bench top method.  Do not remove the PVC threaded fitting if already installed, if not install it now.   Replace it with the PVC cap that has a 1/8th inch tubing fitting with 20 feet of tubing.  Run the other end of tubing out the door of the shelter.
  3. Remove the fan from the bottom port only is you are following the zero bench top method.  Use the other cap and PVC fittings from the kit to completely cover the bottom port.
  4. At this point be sure to cap the NEPH fitting on the AETH/NEPH manifold.
  5. Use the Display toggle switch to choose the Calibration Gas Screen as shown in picture below.  The ratio should read 2.61e+0 for pure CO2.  If it does not read this use the Parameter toggle switch to raise or lower the number under set R-gas to obtain parameter.  Mark this as checked on the calibration form.

  1. Connect the regulator to the CO2 bottle and verify the regulator is leak proof and purged appropriately.
  2. Set the regulator to Zero PSI and the manual flow control valve is closed.
  3. Connect the ¼ inch copper tubing to the pure CO2 span gas regulator.
  4. Connect the other end of the tubing with the critical orifice to the purge port at the rear base of the instrument.
  5. Before opening the pure CO2 main bottle valve, be sure the regulator is adjusted to zero psi.  Now open the main bottle valve to get pressure to the regulator and set the regulator psi to five.
  6. Slowly open the manual flow control valve on the regulator output to full open.
  7. Use the Display toggle switch to obtain Span Calibration Screen shown in picture below.  And enter the Span parameter into the calibration form.

  1. Now that span gas is passing through the instrument allow five minutes to for the bscat to settle down.
  2. Use the Parameter toggle switch to change the set span number to have the bscat and gas lines of this display match each other as closely as possible.  A tolerance of +/- 0.05 should be expected.  You will find that as you make an adjustment you must wait for the bscat data to settle down.  Use one minute intervals to fill in the value portions of the calibration form.  Set the NEPH channel to DAP Integer and obtain the number corresponding to the specification and add this to the DAP integer line of the form.
  3. Fill out the span calibration portion of the form completely.
  4. Once this has been completed the instrument is ready to resume normal operation.
  5. Reconnect all plumbing.
  6. Record and calculate the information called out in the checks after calibration section.
  7. Return all calibration kit supplies into safe storage for later use.
  8. Up all of the Aethalometer & Nephelometer channels.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2:  Setup for Span Calibration Bench Top Method

 

 

 

 

 

Figure 3:  Span Calibration Bench Top Method with pure CO2 bottle connected.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nephelometer Maintenance

 

Cleaning Procedure for the Scattering Chamber

 

  1. Turn power off and disconnect instrument from sample plumbing.
  2. Remove the four 6-32 socket screws from the top of the instrument.  The top is sealed with an O-ring and may require tapping to get loose from the body.  Mark the housing before fully removing it for proper baffle assembly later.  The component you are removing is called the dark trap.  Set this aside.
  3. Using the Zero air in the shelter blow out the scattering chamber; don’t use too much air pressure or the chopper could become damaged.  Blow out all visible debris.
  4. Check carefully with a flashlight for spider webs and debris, especially around the aperture hole.  Even the smallest filament in the scattering cone can cause extremely high scattering background.
  5. Now instrument is ready to be assembled.
  6. Verify the O-ring is in good condition and the mating surfaces do not have burrs on them that could cause light to escape.
  7. Install the dark trap, being careful to align the baffle with the lamp assembly.
  8. Install the four 6-32 socket screws onto the top of the instrument.
  9. Connect the sample tubing back to instrument.  Turn the power back on.

 

Changing the Flash Lamp Assembly

 

Caution – The 2.2uf capacitor inside the flash lamp assembly stores approximately 400vdc, so disconnect power before removing cover.

 

  1. Remove the two 8-32 screws securing the flash assembly cover and remove it.
  2. Remove the four 4-40 socket screws holding the lamp assembly and remove.  You may have to pry the assembly away from the gasket carefully with a screw driver.
  3. The lamp is connected to the flash circuit board with a six pin Amp connector.
  4. Unplug the Amp connector and replace lamp with new assembly.
  5. Once the new assembly has been connected reverse the order to replace the lamp assembly.

 

Nephelometer Analog Calibration

 

Analog calibrations for this instrument are accomplished by using Zero, One and Five volts DC.  At the site the most effective way to do this is to use any C class analyzer as a voltage generator.  On the C class analyzer choose set outputs to Zero, those analyzers analog output green connector voltage changes to 0 volt DC.  Choose Full Scale, the green connector voltage changes to 5 volts DC.  To obtain 1 volt DC for TP and RH cal choose Full Scale and scroll to 20% by using the arrow keys.  Use this to generate the voltages needed for the two point analog calibration.

There are six channels that will or may require calibration.  They are named below.

Cal Channel Values and Voltages for each are:

                                Zero Value             Voltage                  Span Value            Voltage

NEPH                     0                              0                              2e-4                         5

NEPH LOG            0                              0                              1e-3                         5

NEPH IC                0                              0                              1e-3                         5

NEPH LB               3                              0                              5                              5

NEPH TP               -10                           0                              60                            1

NEPH RH               0                              0                              100                          1