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¶

You need to perform a 3-point calibration with the calibration solutions. The solutions vary their pH with temperature, so make sure to check the temperature prior. 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 or use the calculator here.

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:

mid point
low point
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). First, read the sensor multiple times until the reading is stable:
```
control ph com r
3.98
control ph com r
3.98
...
```

Issue the midpoint calibration command:

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

Example at 30°C

control atlas ph com cal,low,4.01

High Point Calibration¶

The same step with High point 10.00 calibration solution (blue). First, read the sensor multiple times until the reading is stable:
```
control ph com r
9.84
control ph com r
9.84
...
```

Issue the midpoint calibration command:

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

Example at 30°C

control atlas ph com cal,high,9.96

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:

set probe type
dry point
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

Readings are 0?

It is normal that if the probe type has been changed (for instance, you are using a K10 probe), that the readings are 0 after setting the probe type.

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:

Single point calibration (dry point)
2-point calibration (dry point and 0 mg/l point) - only if you need accurate readings below 1mg/l

Make sure you have followed the probe reconditioning before proceeding with this calibration.

Datasheet

Here you can find the datasheet:

Calibration info on page 9
Calibration commands on page 52

Example commands (you can put control ox, control oxygen or control dissolved oxygen - however! do not put control dissolved as it will use TDS)

control ox com r
control ox com cal
control ox com cal,0
control ox com cal,clear
control ox 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 ox com P,kPaValue

More information on datasheet, page 57

OPTION 1: Single point calibration¶

First calibrate, compensate later

Temperature, salinity and pressure compensation values have no effect on calibration.

Read the sensor multiple times until the reading is stable:

control ox com r
13.95,50%
control ox 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 ox com cal
```

Be careful

If at any point of the calibration process you see akward readings (for instance, that using a 0mg/l solution for dissolved oxygen you see weirdly high values), it is better to start over. For this, proceed with:

control ox com cal,clear

And start from the beginning.

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 ox com r
13.95,50%
control ox 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 ox 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.

Atlas ORP¶

You only need to perform a single point calibration. You can use any calibrated solution, as long as it's within your sensor range. Atlas uses a 225mV calibration.

Datasheet

Here you can find the datasheet:

Calibration info on page 12
Calibration commands on page 49

Example commands

control orp com r
control orp com cal
control orp com cal,[value]
control orp com cal,clear
control orp com cal,?

Single point calibration¶

Read the sensor multiple times until the reading is stable:
```
control orp com r
225
control orp com r
224
...
```
Issue calibration command
```
control orp com cal,[value of ORP]
```

Example at 25°C

control orp com cal,225

Atlas PT100/1000 Temperature¶

You only need to perform a single point calibration. This process is only necessary if you change the probe cable or the first time you use the sensor.

Datasheet

Here you can find the datasheet:

Calibration info on page 12
Calibration commands on page 53

Example commands (you can put control ox, control oxygen or control dissolved oxygen - however! do not put control dissolved as it will use TDS)

control atlas temp com r
control atlas temp com cal
control atlas temp com cal,[value]
control atlas temp com cal,clear
control atlas temp com cal,?

Warning

This is needed because the temperature probe is a resistive sensor – more cable → more resistance!

Reference

You will need another temperature probe or something of known temperature (like boiling water) that is already calibrated for this. Make sure both are stable before issuing calibration commands!

Single point calibration¶

Read the reference probe multiple times until the reading is stable. Write down the value:
```
control atlas temp com r
22.5
control atlas temp com r
22.4
...
```

Read the target probe multiple times until the reading is stable:

control atlas temp com r
29.5
control atlas temp com r
29.4
...

Issue calibration command:

control atlas temp com cal,[value of temperature from reference probe or temperature]