Atlas Scientific EZO Complete Dissolved Oxygen Meter User Guide

EZO Complete Dissolved Oxygen Meter
User Guide

V 1.0
Released 4/23
EZO Complete-DO™
USB Dissolved Oxygen meter
Users Guide
ISO 5814 Compliant (determination of dissolved oxygen)

EZO Complete Dissolved Oxygen Meter

TENT PROTECTED

Written by Jordan Press Designed by Noah Press This is an evolving document, check back for updates.

The EZO Complete-DO™ has all the features of this bench top meter.

Isolated Power Supply

1 Two decimal D.O. reading
2 Temperature, pressure, and salinity compensation value
3 Percent saturation
4 Milligrams per liter
5 Immediate reading
6 Timed readings| 7 Set device name
8 Voltage usage
9 Multi point calibration
10 Manual temperature compensation
11 Manual pressure compensation
12 Manual salinity compensation
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The EZO Complete-DO™ is compatible with any brand of pH probe.

Interference free

The EZO complete readings are unaffected by other sensors in the same water.

Ingress protection – IP62
The EZO-DO Complete™ is dust proof and resistant to splashing water.
Two areas of concern are the USB connector and the probe connector.

Ingress protection – IP62
An electrical short can occur if water enters the USB connector. A USB short could permanently damage the EZO-Complete. A USB short is not covered under warranty.

A connector short can occur if water enters the SMA connector. A connector short will cause the DO readings to pin to 0, 35, or the probe will respond slowly to changes in  DO. A connector short is reversible and will not damage the EZO-Complete. However, frequent shorts will eventually damage the pH probe.

The SMA connector is part of your probe; Nothing should be in contact with this part.

Do not use this as a mounting point!

Setup

Click here to download Atlas Desktop Monitoring Software
Setup
Once you have installed the Atlas Desktop monitoring software, you can begin monitoring and logging your readings.

Calibration theory

The accuracy of your readings is directly related to the quality of your calibration. (Calibration is not difficult, and a little bit of care goes a long way).
Confirm the D.O. probe is working correctly
Take readings in air first.

Calibrate first, compensate later
Compensating for temperature, pressure, and salinity will change your calibrated readings to a value that cannot easily be predicted. This makes it difficult to know if the probe has been calibrated correctly.

Temp = 20 ºC
Pressure = 101 kPa
Salinity = 0| 9.09 Mg/L
Temp = 29 ºC
Pressure = 93 kPa
Salinity = 5 (too many variables)|

Best practices for calibration

Always watch the readings throughout the calibration process. Issue calibration commands once the readings have stabilized.

Never do a blind calibration!
Issuing a calibration command before the readings stabilize will result in drifting readings.

Calibration order

High point calibration
Remove the Dissolved Oxygen probe’s cap and let the probe sit, exposed to air until the readings stabilize. (small movement from one reading to the next is normal).

After calibration is complete, you should see readings between 9.09 – 9.1X mg/L. (only if temperature, salinity and pressure compensation are at default values)

Low point calibration
After you have calibrated the EZO™ Dissolved Oxygen circuit using the “Cal” command; Remove the top of the Zero Dissolved Oxygen calibration solution pouch, and  Insert the probe and stir it around to remove any trapped air (which could cause readings to go high). Let the probe sit in Zero D.O. calibration solution until readings  stabilize. (small movement from one reading to the next is normal).

Advanced calibration

Probe temperature calibration
Probe temperature calibration ≠ Temperature compensation.
When a Dissolved Oxygen probe is calibrated, it is calibrated to the oxygen level and ambient temperature. As a D.O. probe is heated or cooled, its response curve will  change.
A small temperature change (≤ 5 °C) will not affect the probe. However, a large temperature change will be noticeable.

What to do:
After the Dissolved Oxygen probe has been properly calibrated, another calibration can be done to account for the probe temperature.

Let the probe acclimate to its operating temperature and then recalibrate. Once the probe has been calibrated at its intended operating temperature, using temperature compensation will give accurate readings.

Understanding D.O. measurements

Most chemical sensors do not directly measure the parameter they are designed for. Dissolved oxygen is no exception. A galvanic D.O. probe is actually an oxygen pressure sensor. It only measures the partial pressure of oxygen.
Keep this in mind when choosing a spot to place the probe.

It just so happens that partial pressure of oxygen is the same in water as it is in air.
(While the pressure is the same, the amount is not. Pure water at sea level can only hold ~9 mg/L of oxygen, while the atmosphere holds ~300mg/L)
By comparing oxygens pressure to its solubility in water, the mg/L are derived.
There are three factors that affect waters ability to hold oxygen.
Temperature Salinity Atmospheric Pressure

Temperature
Water temperature has the largest effect; the colder the water, the more oxygen it holds.
As water heats up, its ability to hold oxygen goes down.
Pure water at 1°C can hold 14.2 mg/L
And at 40°C it can only hold 6.4 mg/L

Salinity
When salt is added to water, it drives out oxygen by competing for the same space.
Sea water at 1°C can only hold 10.7 mg/L
Pure water at 1°C can hold 14.2 mg/L

Atmospheric Pressure
A D.O. probe is an oxygen pressure sensor.
Dissolved oxygen pressure cannot be higher than atmospheric oxygen pressure. This is why the probe is calibrated to the atmosphere; it defines the probe’s response to the  maximum oxygen pressure available. However, oxygen pressure does not tell us how much oxygen is available to dissolve in the water. That information is derived from atmospheric pressure (where atmospheric pressure = altitude).
As altitude increases, oxygen concentration decreases, and because D.O. readings are expressed in Mg/L, the oxygen concentration must be known.
At sea level, 1°C pure water can hold 14.2 mg/L
At 1,500 meters, 1°C pure water can hold 11.7 mg/L
At -1,200 meters, 1°C pure water can hold 16.2 mg/L

Hyper saturation with pure oxygen

Dissolved oxygen measurements are based on natural occurring oxygen levels. However, some applications may require pure oxygen to achieve extremely high saturation  levels.
Because injecting pure oxygen into water is not a naturally occurring event, you will need to change some compensation parameters to achieve extremely high readings.
To reach 100mg/L and a saturation of 350%
Set pressure compensation to: 202 kPa
Set temperature compensation to: 1°C

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