1. Luminescence Dissolved Oxygen
Lange LDO™ Sensor
What does LDO means?
Luminescence Dissolved Oxygen
an optical and unique way (patent pending) of measuring Dissolved Oxygen
eliminates nearly all disadvantages of traditional electro chemical DO measurement

2. Lange LDO™ Sensor How does it look like? Photo diode red LED blue LED
Sensor body
Sensor cap
Luminophor
blue LED
red LED
Photo diode

3. Lange LDO™ Sensor How does it works? Sensor Sensor- cap
Luminescence
indicator-
molekules
Sensor-
cap
Sensor
The sensorcap is coated with a luminescent polymer.
For the measurement the blue LED emits a pulse of light.
This passes through the transparent carrier material and transfers part of its radiation energy to this material.
Electrons from the luminophore are in this way raised from their initial energy state to a higher energy level.

4. Lange LDO™ Sensor How does it works? Sensor Sensor- cap
Luminescence
indicator-
molekules
Sensor-
cap
Sensor
The electrons return to the initial state via a number of intermediate levels (within ms)
The energy difference is emitted as a red radiation.
This light is detected by a photo diode.

5. Lange LDO™ Sensor How does it works? Incident blue light
Membrane
Photodiode
LED
Incident blue light
Emitted red light
Sensor cap with O2-selective fluorescing molecules
The intensity of the residual red light is proportional to oxygen concentration
Oxygen from sample

6. Lange LDO™ Sensor How does it works?
If oxygen molecules are now in contact with the luminophore,
these are able to absorb the energy of the electrons in higher energy levels
and make it possible for the electrons to return to their initial state without the emission of radiation.
increasing oxygen concentration results in
a reduction of the intensity of the red radiation emitted.
this causes vibrations in the luminophore, result in electrons leaving the higher energy level more quickly
The lifetime of the red radiation emitted is thus shortened.

7. Lange LDO™ Sensor How does it works?
Both aspects are covered by the term quenching.
Their effects are shown next page: the pulse of light sent out by the blue LED at time t=0 is incident on the luminophore that then emits red light immediately afterwards.
Maximum intensity (Imax) and the decay time for the red radiation are dependent on the surrounding oxygen concentration (the decay time t is defined here are the time between excitation and reduction in the red radiation to 1/e times the maximum intensity).
Intensity curve for blue radiation producing excitation and red radiation emitted. To determine the oxygen concentration the life t of the red radiation is analysed. In this way the oxygen measurement is reduced to a purely physical measurement of the time.

8. Lange LDO™ Sensor t1 t2 How does it works? Sensor cap Luminophor
Normed Intensity
Exitation puls
Sensor
cap
LED
Photo Diode s
Emisson profile
without O2 t1
with O2 t2
Time [µs]
Oxygen
Luminophor

9. „Lifetime of Luminescense“
Lange LDO™ Sensor
How does it works?
The LDO technology reduces the oxygen measurement to a pure time measuement - the
„Lifetime of Luminescense“

10. Lange LDO™ Sensor How does it works? Sensor cap
A red LED is also present in the sensor
The red LED acts as an internal standard (or reference) for a comparison to the red light given off by the luminescent coating.
Between flashes of the blue LED a red LED of known intensity is flashed on the sensor element.
Sensor
cap
LED
Photo Diode

11. Customer benefits Lange LDO™

12. Key features of Lange LDO™
Sales arguments for Lange LDO™
No calibration required
Stable measurement results
Independent from flow rate
Reduced cleaning frequency
Low maintenance efforts
Without interference's
No more poisoning of the sensor
Short response time
No polarisation time
Two year warranty on sensor cap

13. No calibration required
Sales arguments for Lange LDO™
Lange LDO™ sensor is very stable as it does not change it’s relevant characteristics !
No anode to consume and no electrolyte to deplete  extremely stable measurements
Adjustment of the whole optics due to an internal standard (red LED)
Each Lange LDO™ sensor cap is factory calibrated
Background:
 With Lange LDO™ the customer has not to calibrate his DO system anymore!

14. Stable measurement results
Sales arguments for Lange LDO™
Background: - Lange LDO™ technology means no chemical inter action between the sample and the sensor element
- Constant adjustment of all optical parts due to an internal standard (red LED)
 With Lange LDO™ the DO measurement results are stable over a longer period of time and thus more reliable

15. Independent from flow rate
Sales arguments for Lange LDO™
Background: - Electro chemical DO meters consume Oxygen during the measurement
 Constant need for fresh sample and therefore a min. flow rate required
- Lange LDO™ doesn’t consume DO. It requires the presence of a representative DO concentration at the sensor element only
 No flow rate required

16. Reduced cleaning frequency
Sales arguments for Lange LDO™
Background: - No DO consumption during the measurement
- DO has not to diffuse through a membrane
- DO must only be in contact with the luminescent coating on the sensor cap
 Dirt has not the same negative influence with the optical method as with the conventional DO sensors

17. Low maintenance efforts
Sales arguments for Lange LDO™
Background:
 Only a sensor cap has to be exchanged once every two years : screw on / screw off
No membrane to replace
No more stretching of Teflon (very old procedure) and worrying about air bubbles
No electrolyte to foul or poison
No H2S poisoning of the electrolyte
No more punctured membranes
No more electrolyte depletion
No anode or cathode
No more coating of electrodes
No cleaning of anodes

18. Without interference's
Sales arguments for Lange LDO™
Background: - The Lange LDO™ principle is selective to oxygen only.
 No interference with pH swings, waste water
chemicals or heavy metals like open
galvanic cells
 Lange LDO™ is superior compared to (self cleaning) open galvanic DO cells as there are no interference’s

19. No more poisoning of the sensor
Sales arguments for Lange LDO™
Background: - Lange LDO™ principle is not based on a chemical inter action between the sample and the sensor element
- Lange LDO™ has been tested to a broad range of other chemicals. The sensor element is not affected by these (see data sheet)
 Lange LDO™ can measure reliable even in difficult applications

20. Short response time
Sales arguments for Lange LDO™
Background: - With the optical measuring principle DO only has to be present in front of the sensor element and not to diffuse through a thick (50 µm) Teflon membrane.
 Short response time can be programmed (t90 < 30 s) for high dynamic processes

21.  Switch the instrument on and start measuring!
No polarization time
Sales arguments for Lange LDO™
Background: - Lange LDO™ is based on a new, optical
technology. This technology does not need any “warm-up”. It is ready for use immediately.
 Switch the instrument on and start measuring!