LR 925/01
Operating manual
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Ultrapure water conductivity measuring cell
LR 925/01
Note
The latest version of the present operating manual can be found on the
Internet under www.WTW.com.
Copyright © Weilheim 2009, WTW GmbH
Reprinting - even as excerpts - is only allowed with the explicit written
authorization of WTW GmbH, Weilheim.
Printed in Germany.
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LR 925/01 Contents
LR 925/01 - Contents
1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.1 Structure and function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2 Recommended fields of application . . . . . . . . . . . . . . . . . . . . 12
2 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 What to do if... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4 Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1 General data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2 Measuring ranges and resolution . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Accuracy of the IDS measuring technique . . . . . . . . . . . . . . . 16
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Overview LR 925/01
21
1Overview
1.1 Structure and function
Structure
1 Shaft
2 Connecting head with active electronics
Automatic sensor
recognition
The sensor electronics with the stored sensor data is in the connecting head.
The data include, among other things, the sensor type and series number.
With each calibration, the calibration data is written in the sensor and the
calibration history is recorded. The data is recalled by the meter when the
sensor is connected and is used for measurement and for measured value
documentation. Storing the calibration data in the sensor ensures that the
correct cell constant is automatically used if the sensor is operated with
several meters.
The digital transmission technique guarantees the failure-free
communication with the meter even with long connection cables. If the sensor
firmware is enhanced by WTW, it can be updated via the meter.
1.2 Recommended fields of application
Measurements in ultrapure water.
12
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LR 925/01 Cleaning
2 Cleaning
CAUTION
To clean the sensor, disconnect it from the instrument.
Outside cleaning We recommend to clean the sensor thoroughly, especially before measuring
low conductivity values.
Contamination Cleaning procedure
Lime sediments Immerse in acetic acid for 5 minutes (volume
share = 10 %)
Fat/oil Clean with warm water that contains
washing-up liquid
After cleaning, thoroughly rinse with deionized water and recalibrate if
necessary.
Aging of the
conductivity
measuring cell
Disposal We recommend to dispose of the measuring cell as electronic waste.
Normally, the conductivity measuring cell does not age. Special measuring
media (e.g. strong acids and bases, organic solvents) or temperatures that
are too high may considerably reduce its lifetime or lead to damage. The
warranty does not cover failure caused by measuring conditions and
mechanical damage.
3 What to do if...
Error symptom Cause Remedy
No temperature or
conductivity display
Measurement delivers
implausible conductivity
values
– No connection between meter and
conductivity measuring cell
– Cable defective
– Measuring range exceeded
– Contamination in the area of the
electrodes
– Establish connection between
meter and conductivity measuring
cell
– Make sure the correct sensor is
being used for the application
– Clean the conductivity measuring
cell (see section 2).
Incorrect temperature
display
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– Electrodes damaged
– The temperature sensor is not
immersed deep enough in the
measuring solution
– Temperature sensor defective
– Return the sensor
– Observe the minimum immersion
depth
– Return the conductivity measuring
cell
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Technical data LR 925/01
120.0
12.0
176.0
21.7
4 Technical data
4.1 General data
General features Measuring principle 2-electrodes measurement
-1
Cell constant 0.100 cm
Temperature sensor Integrated NTC 30 (30 k: at 25 °C / 77 °F)
Dimensions
(in mm)
± 2 %
Weight Approx. 90 g (without cable)
Materials Shaft Stainless steel 1.4571
Connection head POM
Conductivity electrodes Stainless steel 1.4571
Thermistor enclosure Stainless steel 1.4571
Connection cable Lengths 1.5 m
Diameter 4.3 mm
Smallest allowed
bend radius
Fixed installation: 20 mm
Flexible use: 60 mm
Plug type Socket, 4 pins
Pressure
resistance
Sensor with connection
cable
IP 68 (2 x 10
Cable plug IP 67 (when plugged in)
5
Pa or 2 bar)
14
The LR 925/01 meets the requirements according to article 3(3) of the
directive, 97/23/EC ("pressure equipment directive").
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LR 925/01 Technical data
Measurement
conditions
Conductivity measuring
range
Temperature range -5 ... 70 °C (100 °C) 23 ... 158 °F (212 °F)
Max. admissible
overpressure
Minimum depth of
immersion
Maximum depth of
immersion
(at temperature)
Operating position Any
Storage conditions Recommended storing
method
Storage temperature 0 ... 50 °C (32 ... 122 °F)
Characteristic data
on delivery
Temperature responding
behavior
0.01 μS/cm ... 200 μS/cm
5
2 x 10
Pa (2 bar)
30 mm
Whole sensor + cable up to 70 °C (158 °F)
Sensor shaft only (=120 mm) up to 100 °C
(212 °F)
In air
(99 % of the final value display after)
t
99
<20s
Measuring ranges,
resolution
Accuracy of the temperature
± 0.2 K
sensor
4.2 Measuring ranges and resolution
Measured parameter Measuring range Resolution
ӕ [µS/cm] 0.01 ... 19.99
0.0 ... 199.9
(Resistivity) [kOhm*cm] 5.00 ... 9.99
ρ
10.0 ... 99.9
100 ... 999
(Resistivity) [MOhm*cm] 1.00 ... 9.99
ρ
10.0 ... 99.9
T [°C] − 5.0 ... + 100.0 0.1
0,01
0,1
0.01
0.1
1
0.01
0.1
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Technical data LR 925/01
4.3 Accuracy of the IDS measuring technique
Measured parameter Accuracy (± 1 digit)
ӕ, ρ ± 0.5 % of measured value
T [°C] ± 0.1
16
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