KROHNE BM 70 A User manual

DIN A4: 7.02224.32.00
©KROHNE 01/2001 US size: 7.02224.72.00
GR/LD
This documentation is designed to help the user and/or systems
planning engineer select the optimum instrument type, assess
measurement properties, and plan the mechanical and electrical
installation.
Detailed information on installation, operation and control of type
BM 70 A/P, BM 702 Level-Radar instruments is contained in the
“BM 70 A/P or BM 702 Installation and Operating Instructions” and
the Short Manual “Getting Started with BM 70 A”, which are supplied
together with the instruments.
The structure of this documentation is modelled on the lines of DIN V 19259 V Standard.
Project Engineering
Guidelines
BM 70 A, BM 70 P, BM 702
LEVEL-RADAR
Contents: Page
1 Application range 2
2 Mode of operation and system structure 3
3 Input (measured quantity) 5
4 Output 6
5 Measuring accuracy 11
6 Application conditions 14
7 Design 23
8 User interface 34
9 Power supply 36
10 Certificates and approvals 38
11 Order information 39
12 External standards, codes and directives 40
13 Quality assurance 40

Page: 2 BM 70 X Project Engineering Guidelines 01/2001
1 Application range
The BM 70 A/P, BM 702 Level-Radar gauging system is used for distance, level, volume and reflection
measurement of liquids, pastes, slurries, solids and particulate materials. It can be operated on
storage and process tanks, and also on still wells.
BM 70 P is specially designed for applications on storage tanks with highest precision requirements.
BM 702 is a 2-wire Radar for the simpler applications in storage tanks, process tanks, stilling wells and
side vessels.
Hazardous-duty versions BM 70 A/P, BM 702 Ex are suitable for use in Ex-Zone 0, 1 and 2.
In Germany (and, depending on the respective radio approval, in some other countries as well), its use
is restricted to closed tanks or containers made of metal or concrete. Because of low output, however,
the microwaves are not harmful to humans.
Selection sheet
Application condition BM 702 BM 70 A BM 70 P
Measuring range ≤20 m / 66 ft 99 9
Measuring range 20 ... 35 m / 66 ... 115 ft — 99
Measuring range 35 ... 100 m / 115 ... 328 ft — K —
Storage tanks 99 9
Still wells / reference vessels 99 9
Process tanks with slightly moving surface 99 K
Difficult process tanks (e.g. agitator) — 9—
Large or many disturbing tank internals — 9K
Solids — K —
Extreme measuring accuracy (± 1 mm) — — 9
High measuring stability / repeatability — — 9
Current output 4-20 mA HART®99 9
2-wire connection 9——
Bus connection (RS 485, PROFIBUS-PA, FF) K 99
Legend:
9suitable
— not suitable
K contact KROHNE

BM 70 X Project Engineering Guidelines 01/2001 Page: 3
2 Mode of operation and system structure
2.1 Measurement principle (FMCW Radar)
A radar signal is given via an antenna,
reflected on the measuring surface
and received after a delay time t.
FMCW: Frequency Modulated
Continuous Wave
The FMCW-radar uses a high
frequency signal (∼10 GHz) which
transmit frequency increasing linearly
1 GHz during the measurement
(frequency sweep) (1). The signal is
emitted, reflected on the measuring
surface and received time-delayed (2).
For further signal processing the
difference ∆f is calculated from the
actual transmit frequency and the
receive frequency (3). The difference
is directly proportional to the distance
i.e. a large frequency difference
correspond to a large distance and
vice versa.
The frequency difference is
transformed via a Fourier
transformation (FFT) into a frequency
spectrum and then the distance is
calculated from the spectrum.The
level results from the difference
between tank height and distance.
Linearity of frequency sweeps
The measuring accuracy of a FMCW radar is determined
from the linearity of the frequency sweeps and their
reproducibility. The linearity correction is deduced via
reference measurement of the oscillator. The non-linearity
is corrected up to 98% (BM 702/BM 70 A).
An immediate frequency regulation is necessary with the
BM 70 P device because of the higher demand on the
measuring accuracy.
With the PLL technology (Phase Locked Loop) the signal
frequency is directly recorded as a digital data and the
converter oscillator locks automatically on the right
frequency.
As the transmit frequency is changed during a short time
interval by FMCW radar the transmitted frequency has to
follow the nominal frequency within micro seconds. This
ensues via modern, fast electronic and processors.
∆f
Time signal
Spectrum
t
f
1) Radar frequency is
modulated linearly
2) Delay time due to
wave propagation
3) Resulting difference
frequency
4) Digital signal
processing
5) Level is
calculated
FFT
Microprocessor
control Reference oscillator
Phase
detector
Microwave
oscillator
Loop
filter
Antenna
PLL structure

Page: 4 BM 70 X Project Engineering Guidelines 01/2001
2.2 Signal processing (digital)
The radar signals are further processed digitally by a microprocessor. The processing system is distin-
guished by intelligent procedures taking into consideration plausibilities and history.
2.3 Advantages of radar technology
Compared to alternative level gauging methods, radar technology offers numerous advantages:
•Non-contact measurement
•It is independent of the gas composition and temperature of the tank atmosphere
•Will also work in tank atmospheres containing vapour and dust
•Independent of electrical properties of the product (conductivity, permittivity)
•Independent of product density and pressure
•No radiation hazard
•Extremely high measuring accuracy (version BM 70 P)
2.4 Modularity (signal converter, flange, antenna)
The measuring system consists of the flange system und the signal converter.
The flange system contains the microwave window separating product from pressure, and the antenna
system.
The compact signal converter contains the microwave generator and the entire signal processing
system, including provision of a standardized output signal (4-20 mA or digital interface).
The signal converter can be detached from the flange system under process conditions, without loss
of pressure or escape of product.
Converter
Flan
g
e with micro-
wave window
Antenna s
y
stem
OO
OO

BM 70 X Project Engineering Guidelines 01/2001 Page: 5
3 Input
3.1 Measured quantity (distance, level, volume, reflection)
The primary measured quantity is the distance between a reference point (as standard: tank mounting
flange) and a reflecting surface (e.g. surface of the liquid).
The filling level is determined by allowing arithmetically for the entered tank height.
Volume measurements are possible by entering a conversion table (max. 50 points).
The strength of the reflected signal can be measured for qualitative assessment of the tank product or
its surface (only BM 70 A/P).
3.2 Measuring range [0.5...20/35/40/100 m]
Minimum tank height: 0.5 m (1.64 ft)
The maximum measuring range is for:
BM 70 A 40 m (131 ft), optionally up to 100 m (328 ft)
BM 70 P 35 m (115 ft)
BM 702 20 m (65.6 ft)
Wave-Stick version 20 m (65.6 ft) recommended
The useful range depends on the antenna size, the reflection properties of the tank product,
the installation position, and the presence of interference reflectors (see Sections 6.1 and 7.3).
3.3 Block distance
The block distance is the minimum measured distance between the mounting
flange (reference point) and surface of the tank product.
Recommended minimum values: see sketches.
Horn antenna without still well:
Product surface
Stora
g
e tanks: 10cm/4"; Process tanks: 20cm/8"
Antenna size* = Type3: 22cm/8.7"; Type4: 34cm/13.4";
* Hastello
y
: -3cm/1.2"
Recommended Antenna distance:
Length of any antenna extension used must be added on!
Still well / Wave-Guide: Wave-Stick
Product
Antenna size * = Type1: 11cm/4.4";
Type2: 15cm/5.9"; Type3: 22cm/8.7"
Recommended antenna distance =
30 cm / 12" (BM 702: 50 cm / 20")
(Wave-Guide: no antenna)
* Hastelloy: -3cm (1.2")
Wave-Stick SW: 6cm/2.4"
384 mm/15.1"
Product
max.
200 mm
Standard:
8"
Minimum block distance =
Standard: 184 mm (7.24“)
General: Rod length - 200 mm (7.87“)
3.4 Behaviour when measuring range exceeded
In the event of the level measuring range being exceeded (including flooding) the measured value will
stick at the block distance, which is adjustable.
If the measured level value drops below the range, it will stick at the set lower range limit (distance =
tank height).
Maximum
level
Block
distance

Page: 6 BM 70 X Project Engineering Guidelines 01/2001
4 Output
4.1 Variants
BM 70 A, BM 70 P:
Variant Comments Described
in Section
Ex-e current output HART®Ex-e; active; HART®protocol;
together with switching output and digital input 4.2 + 4.4
Ex-i (IS) current output
HART®intrinsically safe; passive; HART®protocol
(optional with IS switching output) 4.3 + 4.4
Current output Ex-e; active; not communicable 4.5
RS 485 + current output BM70 protocol or ModBus-RTU or HART®4.6 + 4.5
PROFIBUS-PA intrinsically safe; see Supplementary Instructions -
Foundation Fieldbus (FF) intrinsically safe; see Supplementary Instructions -
BM 702:
Ex-i (IS) current output HART®intrinsically safe; passive; HART®protocol 4.3 + 4.4
PROFIBUS-PA intrinsically safe; in preparation -
Foundation Fieldbus (FF) intrinsically safe; in preparation -
All versions with HART®or BM70 protocol can be operated with the PC program PC-CAT
(see Section 7.7.7).
Overview of digital communication possibilities:
BM 70 A
HART specific software
and operating devices
Converter
HART-
HHC
HAR T Commun icat or
HART
FIELDCOMMUNICATIONS PROTOCO L
O
I>>>
F1 F2 F3 F4
AB C D E F GH I
7 8 9
JK L MNO PQ R
4 5 6
ST U VW X YZ/
1 2 3
# % & < > : +
0 . _
*
HART-Master Tank Inventory System
4 ... 20mA
+ HART
Modbus RTU
...........
Other
communication interfaces
RS 485
RS 485
4mA
(
Ex i
)
+ HART
PC-CAT
or
HAR T Commun icat or
HART
FIELDCOMMUNICATIONS PROTOCO L
O
I>>>
F1 F2 F3 F4
AB C D E F GH I
7 8 9
JK L MNO PQ R
4 5 6
ST U VW X YZ/
1 2 3
# % & < > : +
0 . _
*
HART-
HHC
Point-to-point Multidrop

BM 70 X Project Engineering Guidelines 01/2001 Page: 7
4.2 Ex-e current output HART®
Function Level, distance, volume FRQYHUVLRQWDEOHor reflection,
and error identification;
galvanically isolated from digital input and switching output
Current 4-20 mA; without or with error message 2 mA or 22 mA
Accuracy/linearity 0.05 % (rel. 20 mA; at T=20°C/68°F, 100Ωload and rated operating voltage)
Temperature drift ≤100 ppm/K (typically 30 ppm/K)
Load ≤500 Ω
Effect of load impedance ≤0.02 % (rel. 20 mA for RB= 0...500 Ω)
Effect of power ≤0.02 % (rel. 20 mA for UBwithin limits of tolerance)
Hazardous-duty version: Ex e
Note: Together with switching output and digital input
Digital input (terminals 81/82):
Can be used to interrupt the entire measuring procedure (measurements are suspended) or to hot
start the device.
Applicable voltage: 5...28 V DC
Input resistance: ≥1 kΩ
Switching output (terminals 41/42):
Can be programmed as limit switch, alarm contact or error message.
The contact is open in de-energized condition.
Operating data: max. 100 mA / 30 V DC or 30 V AC.
Internal resistance: ≤20 Ω
4.3 Ex-i (IS) current output HART®(type of protection: Ex de [ia])
BM 70 A, BM 70 P:
Function Level, distance, volume FRQYHUVLRQWDEOH or reflection;
and error identification;
passive output (current sink)
Current 4-20 mA; without or with error message 3.6 mA or 22 mA;
4 mA constant, adjustable for HART®-Multidrop
Temperature drift ≤100 ppm/K (typically 30 ppm/K)
Accuracy/linearity 0.05 % (rel. 20 mA; at T = 20°C/68°F, 10 V supply voltage
and rated operating voltage)
Supply voltage U 8-30 V (between terminals 31 and 32)
Load ≤(US- 8 V) / 22 mA (US= external supply voltage)
Effect of supply voltage ≤0.02 % (rel. 20 mA for U = 8...30 V)
Effect of power ≤0.02 % (rel. 20 mA for UBwithin limits of tolerance)
Note: Digital input is not available.
Optional switching output (terminals 41/42):
can be programmed as limit switch, alarm contact or error message.
The contact is open in the de-energized condition.
Operating data: 6...30 V; ILow ≤110mA; ULow ≤2V; IHigh ≤900 µA (U=30V) and IHigh = 200 µA (U=8V)
Ex-i safety limits
Signal circuit in type of protection: Intrinsic Safety EEx ia IIC/IIB or EEx ib IIC/IIB
for connection to a certified intrinsically safe circuit with the following peak values:
Ui= 30 V; Ii= 250 mA; Pi= 1 W
Effective inner capacitance Ci≈0; effective inner inductance Li≈0
BM 702:
Function Level, distance or volume (conversion table); and error identification;
passive output (current sink)
Current 4-20 mA; without or with error message 3.6 mA or 22 mA;
4 mA constant, adjustable for HART®-Multidrop
Temperature drift ≤100 ppm/K (typically 30 ppm/K)
Accuracy/linearity 0.15 % (rel. 20 mA; at T = 20°C/68°F, 24 V terminal voltage)
Supply voltage U 13-30 V (between terminals); Umin dependent on current (see Sect. 9.1)

Page: 8 BM 70 X Project Engineering Guidelines 01/2001
Load ≤(US- 13 V) / 20 mA (US= external supply voltage)
Effect of supply voltage ≤0.02 % (rel. 20 mA for U = 13...30 V)
Ex-i safety limits
Signal circuit in type of protection: Intrinsic Safety EEx ia IIC/IIB or EEx ib IIC/IIB
for connection to a certified intrinsically safe circuit with the following peak values:
Ui= 30 V; Ii= 100 mA; Pi= 1 W
Effective inner capacitance Ci= 11 nF; effective inner inductance Li≈0
4.4 HART®communication
In accordance with the Rosemount Standard, the HART®communications protocol can be used with a
BM 70 A/P, BM 702.
Electrical connection: see Section 7.6.
There are two ways of using the HART®communication:
a) As a point-to point connection between the BM 70 A/P, BM 702 and the HART®Master
equipment.
A BM 70 A/P, BM 702 can be used either with an Ex-e-current output HART®or with an Ex-i (IS)
current output HART®.
HART
Master 4...20 mA
b) As a multipoint connection (multidrop) with up to 15 devices (BM 70, BM 70 A/P, BM 702 or
other HART®equipment), in parallel on a 2-wire bus:
A BM70 A/P, BM 702 is normally used with Ex-i current output, but an Ex-e current output can also
be used (constant 4 mA in both cases.)
HART
Master 4mA 4mA 4mA 4mA
other
HART
device HART
device
other
4.5 Current output, RS 485 version (no communication capability)
Function Level, distance, volume FRQYHUVLRQWDEOH or reflection,
and error identification
Current 4-20 mA; without or with error message 2 mA or 22 mA
Accuracy/linearity 0.3 % (rel. 20 mA; at T = 25°C/77°F, 100Ωload and rated operating voltage)
Temperature drift ≤200 ppm/K (typically 70 ppm/K)
Load ≤250 Ω
Effect of load impedance ≤0.1 % (rel. 20 mA for RB= 0...250 Ω)
Effect of power ≤0.1 % (rel. 20 mA for UBwithin limits of tolerance)
Hazardous-duty version: Ex e
When operated as switching output (digital output):
Function Limit switch, alarm contact or error message
Low state Current < 2 mA
High state Current = 22 mA (when load ≤250 Ω)
No-load voltage ≤18 V

BM 70 X Project Engineering Guidelines 01/2001 Page: 9
4.6 Digital interface RS 485
RS 485 is a bus allowing two-way communication (half-duplex operation) with the BM 70 A/P Level-
Radar. When the computer system sends out a request, the BM 70 A/P transmits: level, distance,
volume (conversion table), reflection, parameters and status.
A PC can configure any BM 70 A/P via the bus (RS 485/RS232 converter required) by means of the
PC-CAT program, provided no Master is active. The maximum cable length - excluding amplifier - is
2000 m (6500 ft).
Transmission rate: 1200 to 38400 bauds
Address: 0 to 255
Protocols: KROHNE Protocol, Modbus RTU, HART®
Add’l information: see "BM70A/P Communication RS 485" instructions
Additional current output: The current output is conductively coupled to the RS 485 interface!
Technical data: see Section 4.5
Note: Switching contact and digital input not available. However, the current
output can be configured as a switching output.
Various bus configurations
A) Connection of a BM 70 A/P as a single RS 485 user:
RS485 connection must
be terminated with 120 ohms
(if necessar
y
insert resistor
between A and B
)
Computer
s
y
stem Bus line (2 shielded wires)
with termination
resistance
120 ohms
B) Connection of several BM 70 A/P in the RS 485 bus system via stubs to the bus cable:
Computer
s
y
stem
...........
RS485 connection must
be terminated with 120 ohms
(if necessar
y
insert resistor
between A and B)
Bus line (2 shielded wires)
with termination
resistance
120 ohms
without
resistance
termination without
resistance
termination without
resistance
termination
C) Connection of several BM 70 A/P in the RS 485 bus system, with bus cable looped through to
further field instruments:
...........
with termination
resistance
120 ohms
without
resistance
termination without
resistance
termination without
resistance
termination
Bus line (2 shielded wires)
Computer
s
y
stem
RS485 connection must
be terminated with 120 ohms
(if necessar
y
insert resistor
between A and B)
Notes:
•If other devices are operated together with the BM 70 A/P Level-Radar on one bus, all devices
must use the same communications protocol (e.g. ModBus devices of different manufacturers, or
BM 70 and TTM70 with KROHNE protocol).

Page: 10 BM 70 X Project Engineering Guidelines 01/2001
•Since signal reflections at the line ends can interfere with communication, both the line beginning
(at the computer system) and the line end (at the last device) should be terminated with the typical
surge impedance of the cable (120 Ω). Inside the BM 70 A/P, changeover can be made between
"high-resistance" und "120 Ω".
4.7 Signal on alarm
Alarm information can be called up via the following interfaces:
•Local display: flashing display, plain text information
•Current output: error signal 2 mA / 3.6 mA or 22 mA
•Switching output: contact opens or closes
•Digital interfaces: interrogation of error flags
4.8 Digital input
The digital input (for electrical data: see Section 4.2) can be used for temporarily "freezing" measure-
ment or for carrying out a hot start. It is only available in the "Ex-e current output HART®" version.
The "freeze" function can be used to blank out larger, temporary interferences, e.g. very slow
agitators, slide gates, ball valve in the still well. The last measured values in each case are present at
the outputs and in the display.

BM 70 X Project Engineering Guidelines 01/2001 Page: 11
5 Measuring accuracy
5.1 Reference conditions
•Temperature = +20°C (68°F)
•Pressure = 1013 mbar abs. (14.69 psia)
•Air humidity = 65%
•Product reflects well (e.g. water) with calm surface
•Tank diameter > 5 m (16.4 ft)
•Mounted at least 1/7 x tank height (BM 70 P: 1/5 x tank height) away from edge of tank
•No interference reflections inside radiation lobe (± 6...9°; see Section 6.1.1)
5.2 Error of measurement
Since the measuring process primarily determines distance, measuring accuracy can only be specified
as a function of the distance. For that reason, all data given in this Section 5 are based on the mea-
sured distance.
BM 70 A:
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40 m
Distance to flange
1
block
distance
Accurac
y
-4
-3.2
-2.4
-1.6
-0.8
0
0.8
1.6
2.4
3.2
4
inch cm
4.8
-4.8
16 33 49 66 82 98 1153131ft
± 0.3 %
± 1 cm (0.4")
BM 702:
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
5 10152025303540m
1
Block-
Accurac
y
-4
-3.2
-2.4
-1.6
-0.8
0
0.8
1.6
2.4
3.2
4
inch cm
4.8
-4.8
Distance to flange
16 33 49 66 82 98 1153131ft
dist.
± 0.3 %
± 1 cm (0.4") ±0.2%

Page: 12 BM 70 X Project Engineering Guidelines 01/2001
BM 70 A Precision (with special calibration and certificate):
Only with antenna type 4 (200 mm / 7.87") or still well 80 - 200 mm dia. (3 - 8")
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40 m
1
± 0.1 %
± 5 mm (0.2")
Distance to flange
block
distance 16 33 49 66 82 98 1153131ft
Accurac
y
-4
-3.2
-2.4
-1.6
-0.8
0
0.8
1.6
2.4
3.2
4
inch cm
4.8
-4.8
= calibration ran
g
e = not verified b
y
calibration
BM 70 P
Only with antenna type 4 (200mm/7.87") or still well 80-200 mm dia. (3-8") +antenna 1S…4S, see 7.2
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40 m
Distance to flange
Accurac
y
1
Block-
distance
± 0.01 %
± 1 mm (0.04")
±
20
mm
30
...
16 33 49 66 82 98 1153131ft
-0.4
-0.32
-0.24
-0.16
-0.08
0
0.08
0.16
0.24
0.32
0.4
inch mm
0.48
-0.48
5.3 Repeatability
Repeatability is equal to half the value for the error of measurement.
5.4 Measured value resolution/hysteresis
Measured value resolution is: 1 mm / 0.04" for BM 70 A and BM 702, and 0.1mm / 0.004" for BM 70 P
Hysteresis is at least 20 times smaller than the error of measurement.
5.5 Transient recovery time
The transient recovery time is determined by the setting parameter "time constant" (1 ... 100 s).
The transient recovery time relative to 1% deviation from the steady-state value is approximately 4.6
times the time constant.
However, in the case of unusually rapid changes in level, the transient recovery time may deviate from
this figure.

BM 70 X Project Engineering Guidelines 01/2001 Page: 13
5.6 Turn-on drift / turn-on characteristics
After the BM 70 A has been switched on, a rough measured value is displayed after about 1 minute.
The first self-calibration is completed after about 2 minutes. Full measuring accuracy is attained after
30 minutes operating time.
The measured value from the BM 70 P and BM 702 is accurate directly after the startup phase
(approx. 1.5 minutes).
Typical turn-on drift (example):
Measured value
Time/min012 30
BM 70 A
BM 70 P / BM 702
5.7 Long-term drift
The long-term drift is within the specified error of measurement.
5.8 Effect of ambient temperature
Temperature coefficient, signal output:
Ex-e current output HART®: < 100 ppm/K (typically: 30 ppm/K)
Ex-i (IS) current output HART®: < 100 ppm/K (typically: 30 ppm/K)
Current output (RS 485 version): < 200 ppm/K (typically: 70 ppm/K)
Digital interfaces: no temperature influence
The temperature has no effect on the measured value since the device carries out regular self-calibra-
tion.
The effect of temperature of the atmosphere above the liguid product results theoretically in - 1ppm/°C
for air.
In respect of proof of temperature influence with the aid of reference measurements in liquid tanks, it
needs to be borne in mind that liquids generally have a high coefficient of volume expansion (organic
liquids: typically 0.15 %/°C)!

Page: 14 BM 70 X Project Engineering Guidelines 01/2001
6 Application conditions
6.1 Installation conditions
See Section 7.3 for selection of optimum antenna type !
6.1.1 Transmission angle
The transmission angle is defined as the angle αto the vertical, in which the power density of the
radar waves assumes half the value of the maximum power density (half-power beamwidth):
6.1.2 Recommendations for positioning on the tank
A) Horn antenna or Wave-Stick without still well
D
>1/7×H, but max. 1/3×D
Antenna Type 3
or Wave-Stick
H
D
Antenna Type 4
H
>1/10×H, but max. 1/3×D
BM 70 P: >1/5×H
αα
s
Antenna
Type Diameter Trans- mission
angle α
Lobe expansion s per
metre distance
Type 4 200 mm/8“ 6° 10 cm / 4“
Type 3 140 mm/5.5“ 8° 14 cm / 5.5“
Type 2 * 100 mm/4“ 12° * 22 cm / 9“
Type 1 * 80 mm/3" 16° * 30 cm / 12“
Wave-Stick 25 mm/1“ 9° 16 cm / 6.3“
Wave-Guide
/ still well 25-200 mm/ 1-8“ Propagation only inside the still well
* Should only be used in still wells; the transmission angle given applies
to line-of-si
g
ht propa
g
ation, i.e. without still well.
Recommended
Distance
from the
tank wall:
If possible, mount the flange
in that way: the axis of the
converter (direction display)
is oriented tangentially to
the tank wall (example): flange
BM 70 A/P, BM 702
converter
tank wall
display

BM 70 X Project Engineering Guidelines 01/2001 Page: 15
measurable
level
min.
Lower measuring range limited Several BM 70 A/P, BM 702 can
when tank has tapered bottom. be operated in one tank.
Do not position in Do not mount dead centre Do not position
tank centreline! on manhole cover! above internals!
(multiple reflections!) (multiple reflections!) (interference reflections!)
If these recommendations cannot be followed due to the tank geometry, please consult KROHNE!
B) Still well or Wave-Guide
Any position of the still well or the Wave-Guide on the tank is allowed.
(For layout: refer also to Section 6.1.4; for block distance: refer to Section 3.3)
Still well application In a side vessel BM 70 A Wave-Guide

Page: 16 BM 70 X Project Engineering Guidelines 01/2001
6.1.3 Mounting on tank fitting
Horn antenna
Should be mounted on the tank fitting as close to the horizontal as possible (deviation ≤± 2°).
Exception: when product surface is not horizontal (e.g. solids), the flange can be aligned roughly parallel to it.
The antenna should project out of the fitting:
Tank nozzle
D
L
An antenna extension should be fitted when the antenna does not project out of the tank nozzle:
Tank nozzle Antenna
extension
Antenna extensions are available from 100 to 2000 mm (4“ to ~80“) in steps of 100 mm (~4“). Several
extensions can be joined up.
Use of a still well or Wave-
Guide is positively recom-
mended for horizontal
cylindrical tanks
(avoidance of multiple
reflections):
Antenna Diameter D Length L
Type 4 200 mm / 8“ 335 mm / 13" *
Type 3 140 mm / 5.5“ 223 mm / 8.8" *
* Hastelloy: - 30 mm / 1.2"
(subject to change without notice)

BM 70 X Project Engineering Guidelines 01/2001 Page: 17
Exception:
When the tank nozzle is symmetrical, the antenna may end in the nozzle in order to enlarge the
measuring range (minimum dead zone to tank cover, see Sect. 3.3 "block distance" and Sect. 5.2
"error of measurement"):
Tank nozzle
Narrow tank nozzle
If the inside diameter of the nozzle is smaller than the diameter of the antenna, and the nozzle is
accessible from the inside of the tank, the antenna can be mounted from the inside with an extension
(not for versions made of titanium or tantalum). The antenna extension should be about 10 cm (4“)
longer than the height of the nozzle.
Tank nozzle Antenna
extension
Wave-Stick
Note the requirements pertaining to diameter and length of the tank nozzle:
min. 50 mm/2"
max. X
Tank nozzle
L
Version Length L Max. hei
g
ht of nozzle X
Standard
w/o plate
Option
384 mm/15.1″
270 mm/10.6″
500…1000 mm/
20 to 40″
150 mm/6″
50 mm/2″
L – 234 mm
L – 9.2″

Page: 18 BM 70 X Project Engineering Guidelines 01/2001
6.1.4 Mounting on still wells
< 5mm
Pressure
< 0.2"
equaliza-
tion hole
Antenna size must A standard Wave-Stick
fit inside diameter. will not function in the
still well !
A Type SW Wave-Stick can
be used for still wells
40-55 mm (1.57“ - 2.2“). Ö
Further requirements concerning still wells:
•The still well must be electrically conductive.
•Minimum inside diameter of well: 40 mm (1.57“) (BM 70 P: 80 mm (3“), better ≥100 mm (4“)).
•If possible, use only smooth, straight still wells. If nevertheless an assembled still well is necessary,
abrupt changes in diameter along the pipe should be less than 1 mm (0.04“). Surface roughness of
the inside of the pipe should not be more than + 0.1 mm (0.004“).
•It is possible to measure through an open ball valve, provided the valve and the pipe adapters
above and below the valve are relatively smooth-walled.
•Level measurements below the end of the still well are not possible.
•To ensure equalization of pressure, drill one or two small holes in the still well above the maximum
filling level.
•If necessary, several holes can be drilled along the whole pipe. All holes must
be deburred. The holes should be as small as possible and spaced wide apart
(Recommendation: see drawing on the right).
•A reference point at the end of the still well is advisable. Use only a rod or
screw of approx. 6 mm (1/4“) diameter. See drawing below.
Antenna
type Outside dia. Ø
1S*
176 mm / 2.99” 80 mm / 3.15“
2, 2S* 100 mm / 3.94“
3
3S* 140 mm / 5.51“ 152 mm / 5.98”
4, 4S* 200 mm / 7.87“
* for BM 70 P
If necessary, turn larger
antenna to size!
Ø max.
10 mm
min.
50 mm /2"
0.4"
6 mm Ø
1/4 "

BM 70 X Project Engineering Guidelines 01/2001 Page: 19
6.1.5 Wave-Guide
The so-called "Wave-Guide" is a pipe of 30 mm (1.18“) outside and 25 mm (0.98“) inside diameter,
that is bolted direct to the BM 70 A flange system (in the same way as an antenna extension). It
functions in the same way as a still well and can be used for clean products. The Wave-Guide is not
practical in conjunction with the BM 70 P as it will not provide high measuring accuracy.
Maximum length:
Ex: max. 3 m / 9.84 ft
Non-Ex: up to 3 m / 9.84 ft without additional support
pipes longer than 3 m/9.84 ft need to be supported at two points.
6.2 Ambient conditions
6.2.1 Hazardous locations
BM 70 A/P Ex is suitable for use in hazardous locations of the following:
Zones: 0, 1, 2
Temperature classes: T6...T2
Danger groups: IIA...IIC
Refer to Section 10 for further information !
6.2.2 Ambient temperature of signal converter
Standard version: -20°C ... +55°C ( -4 to +131°F)
Special version: -40°C* ... +55°C (-40 to +131°F)
* below –20°C/-4°F the LC display will “freeze”, but work normally again at higher temperatures
BM 702i is limited to an ambient temperature of +40°C / 104°F when operated in hazardous areas with
temperature class T5 or T6!
A "BM 70 sunshade“ should be fitted (see Section 7.7.5) when the signal converter is located in the
open and exposed to strong sunshine.
6.2.3 Flange temperature
Minimum: Horn antenna, Wave-Guide (V96 standard): -30°C / -22°F
Horn antenna, Wave-Guide (V96 special version)
only with Kalrez4079 or Kalrez2035: -60°C / -76°F
Wave-Stick with flange plate: -40°C / -40°F
Wave-Stick without flange plate -20°C/ -4°F
Maximum: V96 basic version: +130°C / +266°F
V96 High-temperature version with distance piece and
FFKM gasket (Kalrez 4079 or KLR6375): +250°C / +482°F **
Kalrez 1091 gasket: +250°C / +482°F
Kalrez 2035 gasket: +210°C / +410°F
Viton gasket: +200°C / +392°F
FEP-sheathed gasket: +200°C / +392°F
Wave-Stick PP, permanently: +100°C / +212°F
Wave-Stick, pressure-dependent (see 6.3.5),
with no mechanical loading radial to the rod: up to +150°C / 302°F
Wave-Stick, steam cleaning (CIP, SIP) 30 minutes: max. +160°C / 320°F
** Safety limit: +280°C (536°F)
6.2.4 Ambient temperature limits
Signal converter:
Measuring function OK, but LCD "freezes": min. - 40°C / -40°F
Functional upper limit, for max. 2 hours: max. +70°C / +158°F
Flange system:
see Section 6.2.3
6.2.5 Storage temperature
-20°C ... +60°C (-4 to +140°F)

Page: 20 BM 70 X Project Engineering Guidelines 01/2001
6.2.6 Climate class
Locations exposed direct to open-air climate, D1 Severity in conformity with EN 60654-1
6.2.7 Ingress protection
Signal converter: IP 66 / IP 67 (equivalent to NEMA 6)
6.2.8 Shock resistance
The device withstands the impact test in conformity with EN 61010, Section 8.2 with 0.5 J energy
and the drop test to prEN 50178:1994.
6.2.9 Vibration resistance
Type test conditions: to IEC 68-2-6 and prEN 50178 (10-57 Hz: 0.075 mm (2.95 10-3) / 57-150 Hz: 1g)
6.2.10 EMC
The devices satisfy the requirements of EN 50081-1, EN 50082-2 and the NAMUR Recommendation.
6.3 Product conditions
6.3.1 Physical properties of the products
Physical properties (such as density, viscosity, conductivity, relative permittivity, magnetic properties,
etc.) have no effect on measurement results.
The relative permittivity is merely required to have a minimum value in order to ensure reliable mea-
surements (see Section 6.3.2).
6.3.2 Relative permittivity
The relative permittivity of the product (εr, Epsilon-R, "dielectric constant") determines the strength of
the reflected signal. Measurement results are not affected so long as the reflected signal is strong
enough, but reliability and the maximum measuring range are dependent upon the relative permittivity.
At εr< 4, a stilling well should be used. The minimum relative permittivity of the product is approxi-
mately εr= 1.5.
See also Section 7.3.
If the Wave-Stick is also to take measurements when immersed, εrneeds to be ≥4.
0%
10%
20%
30%
40%
50%
60%
70%
1 1.2 1.6 2 2.5 3.2 4 5 6.3 8 10 12 16 20 25 40 50 63 8032
Dielectric Constant and Reflection Factor
R
εr
Water
Benzene
Toluene
Petrol
Chlorine
Phosgene Methanol LPG Sulfuric acid
Sulfur
Phenol Nitrobenzene Glycol
Paraffin
U S E A B L E R A N G E