Nephelometric or transmittance measuring - The nephelometric measurement at 90° scattered light is advantageous for lower turbidity, whereas the transmission measurement at 180° is beneficial for medium to high turbidity values: With increasing turbidity, restray and scattering effects between particles are growing bigger. The reduction of light intensity in this case leads to a more accurate result than a 90° nephelometric measurement. Therefore, lab meters for high values are equipped with several measuring options: Ratio modes calculate the final result from different measured angles. For ratiometric measurements, there is no specific standard method to be followed; rather, procedures are established by the application or industry.
White light has a higher sensitivity for small particles, however, the inherent coloration of the solution has a stronger disturbing effect in this case. The IR measurement is required by DIN ISO, the white light measuring by US EPA.
Application areas for turbidity measuring
| | Turb® 355 T/IR | Turb® 430 T/IR | Turb® 550/Turb® 550 IR | Turb® 555/Turb® 555 |
| Applications | Portable use for waste-water, surface water and ground water applications | Portable use for all water testing applications incl. drinking water, wine industry, process control Laboratory use: optional for all applica-tions up to 1100 NTU/ FNU with LabStation | Meter for routine and precise measurements | Meter for routine and precise measurements including QC of com-plex samples and high turbidity values. |
| Light source | Tungsten lamp/IR LED | Tungsten lamp/IR LED | Tungsten lamp/IR LED | Tungsten lamp/IR LED |
| Measuring range | 0-1100 NTU/FNU | 0-1100 NTU/FNU | 0-1000 NTU/FNU | 0-10000 NTU/FNU/FAU |
| Calibration | Automatic 1-3 point | Automatic 3 point | Automatic 1-3 point | Automatic 1-5 point |
| Special features | Portable field meter | Portable field meter Calibration interval Calibration documentation Storage for measure values Optional: LabStation, LSdata | AQA Flow-through measurement (unpressurized) | AQA complete with password protection, ratio method for the reduction of interferences; transmission, flow-through measurement (unpressurized/ up to 4 bar) |
Benchtop Turbidimeters
| | Turb® 550 | Turb® 550 IR | Turb® 555 | Turb® 555 IR |
| Measuring principles | Nephelometric | | Nephelometric | |
| Light source | Tungsten lamp
| IR-LED | Tungsten lamp | IR-LED |
Measuring range NTU
FNU
EBC
Nephelos
FAU |
0 ... 1000
–
–
–
– |
0 ... 1000
0 ... 1000
–
–
– |
0 ... 10000
–
0 ... 2450
0 ... 67000
– |
0 ... 10000
0 ... 10000
0 ... 2450
–
0 ... 10000 |
| Resolution | 0.01 NTU from 0.00 ... 9.99
0.1 NTU from 10.0 ... 99.9
1 NTU from 100 ... 1000 | 0.0001 NTU from 0.0001 ... 9.9999 NTU
0.001 NTU from 10.000 ... 99.999 NTU
0.01 NTU from 100.00 ... 999.99 NTU
0.1 NTU from 1000.0 ... 9999.9 NTU |
| Accuracy | ±2% of value or ±0.01 NTU | 0 ... 1000 NTU: ±2% of value or ±0.01 NTU
1000 ... 4000 NTU: ±5% of value
4000 ... 10000 NTU: ±10% of value |
| Reproducibility | ±1% of value or ±0.01 NTU |
| Calibration | Automatic 1...3 point calibration | Automatic 1...5 point calibration |
| Response time | < 3 seconds | < 6 seconds |
| Cuvettes | 28 x 70 mm (1.1 x 2.76 in) round cuvette, 25 ml sample volume |
| AQA functions | Calibration interval monitoring
Calibration protocol | Calbration interval monitoring
Calibration protocol
Password-protected access to calibration and configuration
Time-controlled data transmission |
| Operating temperature | +10 ... +40 °C (50 … 104 °F) | 0 ... +50 °C (32 … 122 °F) |
| Power supply | Plug-in power supply 100 - 240 VAC ±10% / 47 - 63 Hz |
Portable Turbidimeters
| | Turb® 430 IR / Turb® 430 T | Turb® 355 T / 355 IR |
| Measuring principles | Nephelometric (90° scatter) | Nephelometric (90° scatter) |
| Light source | IR-LED/Tungsten lamp | Tungsten lamp/IR-LED |
Measuring range NTU
FNU |
0 … 1100 / 0-1100
0 … 1100 |
0 … 1100
0 … 1100 |
| Resolution | 0.01 from 0.00 … 9.99
0.1 from 10 … 99.90
1 from 100 … 1100 | 0.01NTU from 1 … 9.99
0.1 NTU from 10.0 ... 99.9
1 NTU from 100 ... 1000 |
| Accuracy | 0.01 NTU or ±2 % of the measured value | ±2 % of the measured value or ±0.1 NTU
last decimal place in range 1 … 500 NTU
±3% of the measured value in range 500 … 1100 NTU |
| Reproducibility | <0.5% of the measured value or 0.01 NTU/FNU | ±1% of the measured value or ±0.05 NTU/FNU |
| Calibration | Automatic 3 point calibration | Automatic 1...3 point calibration |
| Response time | Approx. 3 seconds (IR) / approx. 7 seconds (T) | 14 seconds |
| Cuvettes | 28x60 mm (1.10x2.36 in.), 20 ml sample vol | 25x45 mm (0.98x1.77 in), 15 ml sample vol |
| Interface | RS 232, USB via adapter |
Special Functions
Calibration Protocol
Storage; measured value
RS 232
Date/Time
Data evaluation
Rechargeable battery |
Yes
1000
Yes
Yes
Yes
Optional | —
—
—
—
—
— |
| Operating temp. | 0.. +50 °C (32..122 °F) | 0..+50 °C (3..122 °F) |