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Water Sensors Calibration

Patí Científic Workshop

Calibration on the Smart Citizen Kit

The Smart Citizen firmware has built-in support for the calibration of the sensors. In order to calibrate the sensors you will need to use the SCK Shell.

To enable the sensors you just need to plug you board to the Smart Citizen kit aux port and reboot the Smart Citizen Kit and the sensors will be handled by the board.

Warning

When calibrating don't use the normal read sensor command, this command applies temperature/salinity compensation, calibration should be done without any compensation. Instead you should use control sensorName com r and that will return the raw metrics that sensor can provide. On the documentation of each sensor calibration procedure we describe the format of this metrics.

Danger

After finishing the calibration process restart your SCK to start from a clean state.

Atlas PH

The pH value at current temperature can be found on the reference table on the calibration solution bottle. If the current temperature is not on it, use the closest value. You need to perform a 3-point calibration with the calibration solutions.

Datasheet

Here you can find the datasheet:

  • Calibration theory on page 11
  • Commands on page 52

Example commands

control ph com r
control ph com cal,[mid,low,high],value
control ph com cal,clear
control ph com cal,?

3-point calibration

This is the order of the calibration:

  1. mid point
  2. low point
  3. high point

Warning

Always calibrate the mid point first because it calibration erase all the previous calibration done.

Danger

Always clean the probe with distilled water between each calibration

Mid point calibration
  • Put the sensor in the pH 7 calibration solution.

  • Read the sensor multiple times until the reading is stable:

    control ph com r
    6.48
    control ph com r
    6.45
    ...
    
  • Issue the midpoint calibration command:

    control atlas ph com cal,mid,[value of pH at current temperature]
    

Example at 30°C

control atlas ph com cal,mid,6.99 

After this command if you take a pH reading the result should be 7.00 (or very close to it)

Low Point Calibration
  • Repeat the procedure with the Low point 4.00 solution (the red one).
High Point Calibration
  • The same step with High point 10.00 calibration solution (blue)

Extra notes

The command control com cal,? can be used to check the calibration status as explained on datasheet page 52. The answers can be:

  • ?CAL,0 → No calibration done
  • ?CAL,1 → One point calibration done
  • ?CAL,2 → Two point calibration done
  • ?CAL,3 → Three point calibration done

(not tested) If your calibration solutions are not 4, 7 and 10, you can still use them and replace [value of pH at current temperature] by your values.

Atlas EC

You need to perform a 3 step calibration with a dry point and a 2-point calibration with the calibration solutions.

Datasheet

Here you can find the datasheet:

  • Calibration info on page 12
  • Calibration commands on page 55

Example commands

control conductivity com r
control conductivity com K,[probeType]
control conductivity com K,?
control conductivity com cal,[dry,clear,84]
control conductivity com cal,low,1413
control conductivity com cal,high,12,880
control conductivity com cal,?

2-point calibration

This is the order of the calibration:

  1. set probe type
  2. dry point
  3. two-point calibration
Set probe type

Depending on which probe you have (check drawing for reference) you should set the probe type to K 0.1, 1.0 or 10 (new drivers have K1.0 as default):

To set the correct probe type:

control conductivity com K,1.0

and check which type is set:

control conductivity com K,?
?K,1.0

About the sensor

The Electrical Conductivity sensor provides four different metrics:

  • Electrical Conductivity → EC
  • Total Dissolved Solids → TDS
  • Salinity → S
  • Specific Gravity → SG

The data is presented in order and comma separated EC,TDS,S,SG, for instance 0.00,0,0.00,1.000

Dry calibration

Follow the steps below with the dry sensor before introducing it to the calibration solutions. You need to do this step even if the readings in dry state are 0.

  • Read the sensor multiple times until the reading is stable:

    control conductivity com r
    0.00,0,0.00,1.000
    control conductivity com r
    0.00,0,0.00,1.000
    ...
    
  • Issue the dry calibration command:

    control conductivity com cal,dry
    
Low point calibration

You can check the recommended calibration solutions for each probe on the Probetypes drawing (for instance, for K1.0 probe, 12,880uS and 80,000uS are recomended)

  • Read the sensor multiple times until the reading is stable:

    control conductivity com r
    13470,7278,7.76,1.0
    control conductivity com r
    13230,7144,7.61,1.0
    ...
    
  • Issue the low point calibration command. The value to input is the one of the calibration solution, for example 128800:

    control conductivity com cal,low,12880
    

After this command readings will not change.

High point calibration

Repeat this steps with high point calibration solution and when the readings stabilize issue the command. Again, remember that the value to input here is the one from the calibration solution, for instance 80000:

control conductivity com cal,high,80000

After this steps the two point calibration is complete and the readings will change.

Atlas DO

You have two options for this calibration:

  1. Single point calibration (dry point)
  2. 2-point calibration (dry point and 0 mg/L point)

Datasheet

Here you can find the datasheet:

  • Calibration info on page 9
  • Calibration commands on page 52)

Example commands

control dissolved com r
control dissolved com cal
control dissolved com cal,0
control dissolved com cal,clear
control dissolved com cal,?

Pressure compensation

If the sensor is going to be used at more than 10 meters deep into the water Pressure compensation should be set with:

control dissolved com P,kPaValue

More information on datasheet, page 57

OPTION 1: Single point calibration

  • Read the sensor multiple times until the reading is stable:

    control dissolved com r
    13.95,50%
    control dissolved com r
    13.76,49%
    ...
    
  • Issue the calibration command, after this the readings will change. In this case, there is no need to add any value after cal. The sensor will take the current reading as the dry point.

    control dissolved com cal
    

OPTION 2: 2-point calibration

Two point calibration is recommended if you require accurate readings below 1.0 mg/L. After completing the single point calibration procedure put the probe in the calibration solution.

  • Read the sensor multiple times until the reading is stable:

    control dissolved com r
    13.95,50%
    control dissolved com r
    13.76,49%
    ...
    
  • Issue the calibration command. In this case, you have to input the value of the calibration solution too, for example 0:

    control dissolved com cal,0
    

Reset your SCK and you are ready.

Ready to go?

If you want to send the data to the platform, you will need to Advanced Kit Selection. At the moment the closest Kit Blueprint will be #22 BioPV Kit or #31 SCK 2.1 Sea Water in case you are using a SCK2.1 with GPS. You can request in the forum for a custom blueprint with the specific sensors you are using.