Kobold NGM Operating Instructions Manual
Operating Instructions
for
Guided Wave Radar Level Transmitter
(TDR)
Model: NGM
NGM
page 2 NGM K09/0717
We don’t accept warranty and liability claims neither upon this publication nor in
case of improper treatment of the described products.
The document may contain technical inaccuracies and typographical errors. The
content will be revised on a regular basis. These changes will be implemented in
later versions. The described products can be improved and changed at any time
without prior notice.
NGM
NGM K09/0717 page 3
1. Contents
1. Contents ....................................................................................................... 3
2. Note .............................................................................................................. 4
3. Instrument Inspection .................................................................................... 4
4. Regulation Use ............................................................................................. 4
5. Operating Principle ....................................................................................... 5
6. Mechanical Connection ................................................................................. 5
6.1 Mounting .............................................................................................. 5
6.2 Extended temperature range ............................................................... 6
6.3 PTFE coated single rod probe ............................................................. 7
6.4 Mounting considerations ...................................................................... 7
6.5 Cable entries and cable glands ........................................................... 9
7. Electrical Connection .................................................................................. 10
7.1 Wiring ................................................................................................ 10
8. Operation / Configuration / Adjustments ..................................................... 12
8.1 Control Elements ............................................................................... 12
8.2 Configuration single rod probe or wire rope probe ............................. 14
8.3 Configuration Coaxial probe .............................................................. 17
8.4 probe length and measuring range .................................................... 18
8.5 disturbance signal scan ..................................................................... 19
8.6 Guide to communicating from a PC to a NGM probe ........................ 20
(Configuration of device specific parameters) ............................................. 20
9. Technical Information .................................................................................. 46
10.Order Codes ............................................................................................... 48
11.Dimensions ................................................................................................. 49
12.Safety Instructions for Ex-Versions Model NGM ......................................... 53
13.EU Declaration of Conformance ................................................................. 59
14.ATEX Certificate ......................................................................................... 60
Manufactured and sold by:
Kobold Messring GmbH
Nordring 22-24
D-65719 Hofheim
Tel.: +49(0)6192-2990
Fax: +49(0)6192-23398
E-Mail: info.de@kobold.com
Internet: www.kobold.com
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2. Note
Please read these operating instructions before unpacking and putting the unit
into operation. Follow the instructions precisely as described herein.
The devices are only to be used, maintained and serviced by persons familiar
with these operating instructions and in accordance with local regulations
applying to Health & Safety and prevention of accidents.
When used in machines, the measuring unit should be used only when the
machines fulfil the EC-machine guidelines.
This quick installation guide gives instructions for mounting, wiring, and basic
configuration of NGM. This will be sufficient to achieve a fully functional sensor in
most applications. For further details and advanced configuration of NGM, please
contact your local distributor or KOBOLD directly.
3. Instrument Inspection
Instruments are inspected before shipping and sent out in perfect condition.
Should damage to a device be visible, we recommend a thorough inspection of
the delivery packaging. In case of damage, please inform your parcel service /
forwarding agent immediately, since they are responsible for damages during
transit.
Scope of delivery:
The standard delivery includes:
Guided Wave Radar Level Transmitter model: NGM
Operating Instructions
4. Regulation Use
Any use of the Guided Wave Radar Level Transmitter, model: NGM, which
exceeds the manufacturer’s specification may invalidate its warranty. Therefore,
any resulting damage is not the responsibility of the manufacturer. The user
assumes all risk for such usage.
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5. Operating Principle
NGM uses TDR (Time Domain Reflectometry) technology, which is also known
as Guide Microwave or Guided Wave Radar. This means that low-energy and
high-frequency electromagnetic impulses, generated by the sensor’s circuitry, are
propagated along the probe which is immersed in the liquid or solid to be
measured.
When these impulses hit the surface of the media, part of the impulse energy is
reflected back up the probe to the circuitry which then calculates the level from
the time difference between the impulses reflected.
The sensor can output the analysed level as 4...20 m analogue output, or it can
convert the values into freely programmable switching output signal.
6. Mechanical Connection
6.1 Mounting
In case NGM is delivered with a detached probe, attach the probe onto the small
threaded stud below the hexagon. Ensure that you mount the counter nut first to
secure the probe connection: it has to be interlocked against the probe, NOT
against the plastic of the feedthrough (this would result in sheering off the small
threaded stud; permanently damaging the sensor).
Figure1: mounting
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NGM is mounted vertically to the tank via its connection thread, which is screwed
directly into a standard threaded tank connection, i.e. weld-in socket, or it can be
screwed into a flange, which is then connected to a tank nozzle.
NGM should not be welded directly into the tank. Neither should flanges be
welded onto NGM. Welding on the metal parts of NGM will cause serious
damage to the sensor.
Do not lift or handle NGM by its probe; this can cause excessive stress on the
probe connection. NGM should be handled by the hexagon or the lower section
of the housing. Do not screw in NGM by its housing; it should be tightened only
via its hexagon (wrench size 32mm).
Tighten the coaxial probe only at its lower hexagon; the upper hexagon of the
coaxial probe is not needed for mounting.
The customer has to ensure proper sealing of the sensor connection; based on
his process conditions like temperature, pressure and resistance against his
process liquids and atmosphere.
G thread connections require a suitable gasket for pressure-tight joints.
The G3/4A connection thread of NGM is supplied with a gasket made of Klingersil
C-4400, thickness 2mm. The suggested tightening torque for this thread size, this
type of gasket, and a process pressure of max. 40bar is 25Nm (maximum
permissible torque: 45 Nm).
For NPT thread connections, pressure-tight joints require a sealant directly on the
threads.
6.2 Extended temperature range
NGM with the extended temperature option must be properly included into the
tank insulation to prevent excessive temperatures at the sensor housing due to
thermal radiation or convection, as well as prevention of condensate formation .
However, the insulation layer should not reach higher than the hexagon nut; the
cooling fins of the radiator-style temperature extension have to be outside the
insulation in order to function properly. If necessary, adjust the height of the
mounting socket or nozzle accordingly.
Figure 2: extended temperature option
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6.3 PTFE coated single rod probe
PTFE coated probes must be handled carefully to prevent damage to the coating.
For detailed instruction show to mount a PTFE coated NGM, please contact your
local distributor or KOBOLD directly.
Figure 3: single rod probe, PTFE coated
6.4 Mounting considerations
The probes should be installed so that they are not directly impacted by liquids
flowing out of the filling inlet.
They should neither touch nor sway towards other objects inside the tank or the
tank/nozzle walls; e.g. by agitator swirls. In applications with very strong fluid
movements, which can also cause excessive lateral force on the probe, it is
recommended to anchor the probe. The anchoring fixtures are customer
supplied.
For further details about mounting NGM or if you would like to anchor the probes,
please contact your local distributor or KOBOLD directly.
single rod / wire rope probe
coaxial probe
nozzle diameter
-
1
>50mm
nozzle height
-
<300mm
clearance to tank wall or other internal objects
-
>100mm
clearance between probe end and tank bottom
-
>2mm
diameter of bypass chamber / stilling well
-
2
>25mm
- = no restrictions
1
enough diameter to fit in the coaxial tube (Ø17,2mm)
2
enough diameter to fit in the coaxial tube (Ø17,2mm) and enough room around
the probe for the liquid to flow in and out of the bypass chamber / stilling well
Figure 4: mounting considerations
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The single rod probe is suitable for a very wide range of applications in liquids,
but the signal has a wider detection radius around the rod. Thus, it is more
responsive for measurement signal disturbances which can be easily overcome
by observing a few mounting considerations (see Fig.4) and making simple
configuration adjustments to the sensor.
Caution! While using single rod or wire rope probes, activating the
powerful disturbance signal suppression feature is strongly
recommended.
However, those work most efficiently on stationary interference targets like tall
and narrow nozzles or close-by objects. In case that non-stationary interference
targets close to the single rod probe, like slowly rotating agitator blades, cause
problems with the measurement, it is recommended to use the coaxial probe.
The single rod probe is also the recommended probe type for mounting NGM into
bypass chambers or stilling wells. In this case, plastic centering disks are needed
to prevent the probe from contacting the wall. Please contact your local distributor
or KOBOLD directly for further details.
covered Probe length
6m 12m 20m
Tank Ø
materia
l
3m 6m 9m 3m 6m 9m 3m 6m 9m
Wheat 0,7 0,8 0,9 2 2,7 3 4,1
- -
Corn 0,6 0,7 0,8 1,8 2,4 2,7 3,7
- -
Rice 0,5 0,7 0,7 1,5 2,1 2,4 2,8 4,5
Flour 0,3 0,4 0,4 1,1 1,3 1,5 2,4 3,3 3,7
Sugar 0,7 1 1 1,9 2,8 3,4 3,4
- -
Silica sand 1,1 1,4 1,5 3,2 4,5
-
- - -
Cement 1,2 1,5 1,7 3,2 4,7
-
- - -
Alumina 0,9 1,1 1,3 2,3 3,5 4,2 4,3
- -
Phosphate
fertilizer
1,8 2,3 2,6 5
- -
- - -
Fly ash 1 1,3 1,4 2,5 3,9 4,7 4,7
- -
Coal dust 0,7 0,9 1 1,8 2,7 3,3 3,3
- -
Plastic pellets 0,4 0,5 0,5 1 1,5 1,7 1,9 3,2 4
- = exceeds the max. tensile load of NGM: 5kN.
Figure 5: approx. pulling forces [kN]
Above figures are guidelines to estimate the approx. pulling forces from freeflowing solids acting on a suspended 4mm wire rope probe without any anchoring
in a metal tank with smooth walls
The wire rope probe is recommended for installations in solids, tall tanks and
where limited headroom is available. Its performance characteristics and
mounting considerations are similar to the single rod probe.
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NGM K09/0717 page 9
In addition, please consider the following advice when using NGM in solid
applications:
The bulk solid inside the tank or silo can exert a considerable tensile load on the
wire rope probe, depending on properties of the bulk solid, tank dimension sand
covered probe length (see Fig. 5). This can lead to considerable downwards
pulling forces on the tank roof, which has to be able to withstand the max. tensile
load of NGM: 5kN
It is recommended that the tank be empty during installation. This ensures that
the probe hangs down straight and does not get entangled. After installation also
regularly check if the wire rope probe got entangled or unbraided
Some bulk solids easily form build-up on the tank wall or on internal structures.
This will interfere with the measurements. Choose a mounting position where the
wire rope probe is not in contact with, or close to, such product build-up
For anchoring the wire rope probe in solid applications, please contact your local
distributor or KOBOLD directly
The coaxial probe does not have restrictions regarding mounting position, tank
connection, and proximity to the tank wall or other objects inside the tank.
The coaxial probe is recommended for installing NGM into a non-metallic tank or
open pit. If that is not possible, single rod or wire rope probes can be used when
NGM is mounted into at least a DN50 metal flange or screwed into a metal sheet
with at least Ø150mm.
Figure 6: cable entries
6.5 Cable entries and cable glands
The housing has two cable entries and can be ordered with assembled standard
screw plugs and cable glands. Nevertheless, the customer has to confirm the
suitability of those cable glands for his specific application requirements and
cabling; and replace them when necessary.
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Both cable entries can be fitted with cable glands or suitable conduit systems. If
only one cable gland is fitted, it is recommended to use cable entry D2 (see Fig.
6). Then cable entry D3 has to be closed with a suitable screw plug.
IP68-rated screw plugs and cable glands have to be properly sealed and have to
be properly tightened around cable of suitable type and diameter to ensure the
IP68 rating of the housing.
Cable entries with metric threads can be sealed by mounting the suitable screw
plug or cable gland with matching rubber washers underneath.
Cable entries with NPT threads require a sealant directly on the thread of the
screw plug or cable gland.
For M20x1,5 cable entries, NGM comes assembled with:
1 x cable gland M20x1,5, IP68, nylon PA66, for non-armoured cable Ø5…9mm,
with EPDM washer, max. tightening torque 6Nm on all hexagons, wrench size
24mm. For protection during shipment it is closed with an EPDM sealing plug
which has to be removed for cabling
1 x screw plug, IP68, M20x1,5, nylon PA66, with EPDM washer
For ½” NPT cable entries, NGM comes assembled with:
2 x screw plug, 1/2" NPT, PE-LD. They are not IP68 and are only for housing
protection during shipment. They have to be replaced by the customer
When wiring with shielded or armoured cable, suitable cable glands have to be
used. The contact between the metal housing and the shielding of the cable is
made by using a suitable EMC-type cable gland. Ground the shielding of the
cable only on the sensor side; not on the supply side.
7. Electrical Connection
7.1 Wiring
Figure 7: lower sticker on the black plastic cartridge
Verify that the power supply for the sensor is switched off.
Establish an equipotential connection (potential equalization) between the
external earth terminal of NGM and the closest ground potential terminal of the
tank.
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NGM K09/0717 page 11
Open the housing cover by turning it counter clockwise. It may be necessary to
loosen the cover locking screw with an allen key size 1,5mm. The cover has a
safety chain to prevent it from falling to the ground after being unscrewed.
The lower sticker on the black plastic cartridge inside the housing gives
instructions for the standard M20x1,5 cable gland (Fig. 7). When other cable
glands are being used, their details have to be observed instead.
Loosen the cable gland and pull the cable through the cable gland into the
housing. Pull it far enough to have a convenient length for stripping and handling
the cable.
Install cable with a drip loop outside the housing where the bottom of the loop
must be lower than the cable entry of the housing.
Dismantle the cable carefully and strip the wires as indicated on the sticker.
The stripped wire ends are connected to the sensor electronic via the green
screw less, cage clamp terminal block. It can accommodate stranded and solid
wires 0,5…2mm² / AWG 22...14. The usage of cable end sleeves with insulation
collar is not recommended.
Simply press an orange lever straight down with a small flat tip screwdriver, insert
a stripped wire end into the terminal hole, and release the orange lever; the wire
is now connected.
The upper sticker inside the housing illustrates the inputs and outputs if the
sensor. Connect all wires accordingly, as indicated in Fig. 8.
Pull the cable back, but make sure its mantle does not retract into the cable
gland.
Tighten the cable gland to ensure proper sealing function.
Switch on the power supply for the sensor.
The sensor LED should start blinking green within 6 seconds after connecting the
power (during this start-up time the LED is solid green). The blinking green LED
indicates that the sensor is in measuring mode and working correctly.
Do not tighten the housing cover yet. Some basic configuration is still to be
done…
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page 12 NGM K09/0717
Figure 8: wiring
8. Operation / Configuration / Adjustments
8.1 Control Elements
Figure 9: Control Elements
power supply
control system,
e.g. DCS or PLC
HART modem
computer
DIP switch
push button LED
off/0
on/1
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NGM K09/0717 page 13
Basic configuration of NGM can be done directly on the device via three control
elements: a DIP switch, a single push button and a LED for visual feedback. All
settings required to get NGM fully operational can be performed directly on the
device; or NGM can be ordered completely pre-configured.
All three control elements are enclosed in the black plastic cartridge inside the
housing.
The DIP switch has 8 small white levers. Small numbers from 1 to 8 are printed
underneath the levers: they indicate the DIP switch positions and correspond to
the ones in Fig.9.
The upper position of a lever is off/0 and the lower position is on/1. On the left
side of the DIP switch is also a small indication of the on/1 state.
The off/0 and on/1 states of the DIP switch correspond to the 0/1 indications in
Fig.9.
The upper sticker on the black plastic cartridge shows three colour segments
close to the DIP switch: red, grey, and blue; they correspond to the coloured rows
in Fig.10.
red: indicates DIP switch position 8 which switches between measuring and
configuration mode. Only when DIP switch position 8 is on/1, NGM can be
configured; configuration mode is indicated by the LED blinking alternately green
and red.
When DIP switch position 8 is off/0, NGM is in measuring mode; indicated by the
LED blinking green.
It is only possible to enter the configuration mode when DIP switch positions 1 to
7 are off/0 before setting DIP switch position 8 to on/1; otherwise the LED is
blinking red to indicate an error
blue: indicates the DIP positions through which groups of functions are selected,
e.g. all functions related to the analog current output or the switching output
grey: indicates the DIP positions through which individual functions/configuration
settings are selected
When entering into configuration mode, always start from DIP switch position 8
and move towards position 1.
When exiting configuration mode, always set back all the DIP switch positions to
0, starting from position 1 and move towards position 8.
After setting all DIP switch positions to represent the 0/1 sequence of the desired
function (as described in Fig.10), the push button has to be pressed to execute
the desired function. Execution of the function is indicated by the LED remaining
green until the function has been properly executed, in which case the LED
returns to blinking alternately green and red.
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page 14 NGM K09/0717
DIP switch Position
1 2 3 4 5 6 7 8
DIP switch settings description
0 0 0 0 0 0 0 0 measuring mode
0 0 0 0 0 0 0 1 configuration mode
function group 1 analog current output
0 0 0 1
0 0 1 1
lower range value [4mA]; span 0%
0 0 1 0 upper range value [20mA]; span 100%
0 1 0 0 response time 0,5s[default]
0 1 0 1 response time 2s
0 1 1 0 response time 5s
function group 2 switching output
0 0 1 0
0 1 0 1
lower threshold
0 0 1 1 upper threshold
0 1 0 0 NC [default]
0 1 0 1 NO
function group 3 disturbance signal suppression
0 0 0 1
0 1 1 1
perform disturbance signal scan
0 0 1 0 disturbance signal scan: do not utilize
0 0 1 1
disturbance signal scan: utilize[default]
1
0 1 0 0
upper dead band: short [default]
2
rod probe: 30 mm3
coaxial probe: 0 mm
3
0 1 0 1
upper dead band: medium
rod probe: 190 mm
3
coaxial probe: 160 mm3
0 1 1 0
upper dead band: long
rod probe: 390 mm
3
coaxial probe: 360 mm3
1 0 0 0 amplitude threshold: low[default]
1 0 0 1 amplitude threshold: medium
1 0 1 0 amplitude threshold: high
1 1 0 0 coaxial probe
1 1 0 1 single rod / wire rope probe
function group 4 reset
0 0 0 1 1 0 0 1 reset to delivery configuration
function group 5 measure probe length
0 0 0 1 1 0 1 1 measure probe length
1
for single rod and wire rope probes with a probe length [L] >5.500mm only the top 5.500mm of the probe get scanned for
disturbance signals
2
for single rod and wire rope probes with a probe length [L] >3.000mm the default setting is upper dead band: long
3
determined at reference point (sealing surface of connection thread, see dimensional drawing)
Function groups 4 and 5 require the push button to be pressed and held for at
least 10 seconds for the functions to be executed.
Figure 10: DIP switch settings
8.2 Configuration single rod probe or wire rope probe
For most standard applications, executing the three basic configuration steps
below issufficient to achieve a fully functional sensor; providing a continuous level
measurement through its analog current output.
For further details and advanced configuration of NGM, please contact your local
distributor or KOBOLD directly.
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NGM K09/0717 page 15
8.2.1 perform disturbance signal scan
NGM has to be mounted in its final position and the tank has to be
completely empty in order to perform a disturbance signal scan
set the DIP switch positions to the 0/1 sequence in Fig. 11on the left; start
from position 8 and move towards position 1!
LED will blink alternately green and red
press the push button
LED will remain green for a few seconds while the disturbance signal scan
is being performed
once the scan is completed successfully, the LED will return to blinking
alternately green and red
DIP switch Position
1 2 3 4 5 6 7
8
DIP switch settings description
0 0 0 1 0 1 1
1 perform disturbance signal scan
Figure 11: perform disturbance signal scan
8.2.2 lower range value [4MA]; span 0%
fill the liquid into the tank up to the level where you want to position the
lower range value [4mA]; span 0%.
It is recommended that the lower range value stays within the measuring
range [M]
change DIP switch position 6 to off/0
press the push button
LED will remain green briefly while the lower range value setting is being
executed
once it has been executed successfully, the LED will return to blinking
alternately green and red
DIP switch
Position
1 2 3 4 5 6 7 8
DIP switch
settings
description
0 0 0 1 0 0 1 1
lower range value [4mA]; span
0%
Figure 12: lower range value [4mA]; span 0%
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page 16 NGM K09/0717
8.2.3 upper range value [20MA]; span 100%
raise the liquid inside the tank up to the level where you want to position
the upper range value [20mA]; span 100%.
It is recommended that the upper range value stays within the measuring
range [M]
change DIP switch position 3 to on/1
change DIP switch position 4 to off/0
press the push button
LED will remain green briefly while the upper range value setting is being
executed
once it has been executed successfully, the LED will return to blinking
alternately green and red
set all the DIP switch positions to 0 as indicated in Fig.14on the left; start
from position 1 and move towards position 8!
the LED will change to blinking green
DIP switch Position
1 2 3 4 5 6 7 8
DIP switch settings description
0 0 1 0 0 0 1 1 upper range value [20mA]; span 100%
Figure 13: upper range value [20mA]; span 100%
Tighten the housing cover properly by turning it clockwise; make sure the cover
safety chain does not tangle up. If desired, tighten the cover locking screw with
an allen key size 1,5mm.
DIP switch Position
1 2 3 4 5 6 7
8
DIP switch settings description
0 0 0 0 0 0 0
0 measuring mode
Figure 14: measuring mode
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NGM K09/0717 page 17
8.3 Configuration Coaxial probe
The coaxial probe has a very robust and reliable measurement performance in
almost any application without further configuration. For basic configuration only
the range values for the analogue current output have to be set.
For further details and advanced configuration of NGM, please contact your local
distributor or KOBOLD directly.
8.3.1 lower range value [4MA]; span 0%
set the DIP switch positions to the 0/1 sequence in Fig.15on the left; start
from position 8 and move towards position 1!
lower the liquid inside the tank down to the level where you want to
position the lower range value [4mA]; span 0%.
It is recommended that the lower range value stays within the measuring
range [M]
press the push button
LED will remain green briefly while the lower range value setting is being
executed
once it has been executed successfully, the LED will return to blinking
alternately green and red
DIP switch Position
1 2 3 4 5 6 7
8
DIP switch settings description
0 0 0 1 0 0 1
1 lower range value [4mA]; span 0%
Figure 15: lower range value [4mA]; span 0%
8.3.2 upper range value [20MA]; span 100%
raise the liquid inside the tank up to the level where you want to position
the upper range value [20mA]; span 100%.
It is recommended that the upper range value stays within the measuring
range [M]
change DIP switch position 3 to on/1
change DIP switch position 4 to off/0.
press the push button
LED will remain green briefly while the upper range value setting is being
executed
once it has been executed successfully, the LED will return to blinking
alternately green and red
set all the DIP switch positions to 0 as indicated in Fig.17on the left; start
from position 1 and move towards position 8!
the LED will change to blinking green
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page 18 NGM K09/0717
DIP switch Position
1 2 3 4 5 6 7 8
DIP switch settings description
0 0 1 0 0 0 1 1 upper range value [20mA]; span 100%
Figure 16: upper range value [20mA]; span 100%
Tighten the housing cover properly by turning it clockwise; make sure the cover
safety chain does not tangle up. If desired, tighten the cover locking screw with
an allen key size 1,5mm.
DIP switch Position
1
2 3 4 5 6 7 8
DIP switch settings description
0 0 0 0 0 0 0 0 measuring mode
Figure 17: measuring mode
8.4 probe length and measuring range
The reference point for definition of the probe length [L] is always the shoulder of
the connection thread. The probe length [L] is an important mechanical dimension
which is needed to make sure the probe physically fits into the tank at the
anticipated mounting location; it is not equal to the actual measuring range [M] of
the sensor!
TDR level sensors have small inactive areas at top [I1] and bottom [I2] of the
probe. Those are due to the presence of unavoidable signal disturbances at both
ends of the probe. In these inactive areas the measurements are non-linear or
have reduced accuracy. Therefore, it is not recommended to actually measure
level within those inactive areas. Their length depends on the probe type and the
reflectivity (i.e. dielectric constant) of the liquid to be measured.
The measuring range [M] of NGM extends between the top and bottom inactive
areas of the probe; this is the area in which NGM will have the specified
measurement performance. It is recommended that the maximum and minimum
liquid levels to be measured in the tank are actually within the measuring range
[M] of the sensor. The span between the lower range value [4mA] and the upper
range value [20mA] of the analog current output is equal to 0...100% of your
continuous level measurement reading. It is recommended that the span between
those two range values stays within the measuring range [M].
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NGM K09/0717 page 19
Figure 18: probe length and measuring range
8.5 disturbance signal scan
The disturbance signal scan is a powerful disturbance signal suppression feature
of NGM. The sensorscans its entire probe length for any disturbance signals in
the application that could potentially be misinterpreted as level readings,
memorizes and suppresses them during operation; that way NGM only
recognizes the actual level signals caused by the liquid to be measured.
The disturbance signal scan is intended for the single rod probe, since its signal
has a wider detection radius around the rod, making it more responsive for
measurement signal disturbances.
The disturbance signal scan works most efficiently on stationary interference
targets like tall and narrow nozzles or close-by objects. Thus, NGM has to be
mounted in its final position and the tank has to be completely empty in order to
perform a disturbance signal scan; that will ensure a reliable identification of the
actual disturbance signals only. In case that non-stationary interference targets
close to the single rod probe, like slowly rotating agitator blades or streams of
liquid being filled into the tank, cause problems with the measurement, it is
recommended to use the coaxial probe.
Performing a disturbance signal scan is the prerequisite for utilizing this feature of
NGM.
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