KROHNE BM 70 M Series User manual

Installation and
operating instructions for
BM 70 M
Inclusive Part 2
Supplementary Installation and
operating instructions for
BM 70 M-EEx / BM 70 Mi-EEx
©KROHNE 08/2002 7.10027.21.00
GR
Variable area flowmeters
Vortex flowmeters
Flow controllers
Electromagnetic flowmeters
Ultrasonic flowmeters
Mass flowmeters
Level measuring instruments
Communications engineering
Engineering systems & solutions
Switches, counters, displays and recorders
Heat metering
Pressure and temperature

2 BM 70 M
Part 1: Installation and operating instructions for BM 70 M
1 Range of applications.....................................................................................................................................................5
2 Mode of operation and system structure......................................................................................................................5
2.1 Operating principle (FMCW-Radar) ..................................................................................................................................5
2.2 Signal processing (digital).................................................................................................................................................6
2.3 Modularity (signal converter, flange, antenna)..................................................................................................................7
3 Input .................................................................................................................................................................................7
3.1 Measured variable (distance, level, volume, reflection)....................................................................................................7
3.2 Measuring range...............................................................................................................................................................7
3.3 Block distance...................................................................................................................................................................8
3.4 Out-of-range performance.................................................................................................................................................8
4 Output ..............................................................................................................................................................................8
4.1 Variants.............................................................................................................................................................................8
4.2 Ex-e current output HART®...............................................................................................................................................9
4.3 Ex-i current output HART®(type of protection: Ex de [ia]) ..............................................................................................10
4.4 HART®communication ...................................................................................................................................................10
4.5 Current output (non-communicable) ...............................................................................................................................11
4.6 Digital interface RS 485 ..................................................................................................................................................11
4.7 Breakdown signal............................................................................................................................................................12
4.8 Digital input .....................................................................................................................................................................13
5 Measuring accuracy......................................................................................................................................................13
5.1 Reference conditions ......................................................................................................................................................13
5.2 Error of measurement.....................................................................................................................................................13
5.3 Repeatability ...................................................................................................................................................................14
5.4 Measured value resolution/hysteresis.............................................................................................................................14
5.5 Transient recovery time...................................................................................................................................................14
5.6 Long-term drift.................................................................................................................................................................14
5.7 Effect of ambient temperature.........................................................................................................................................14
6 Operating conditions....................................................................................................................................................14
6.1 Installation conditions......................................................................................................................................................15
6.1.1 Transmission angle.........................................................................................................................................................15
6.1.2 Recommendations for positioning on the tank................................................................................................................15
6.1.3 Mounting on tank fitting...................................................................................................................................................17
6.1.4 Mounting on stilling wells/ trunks.....................................................................................................................................18
6.1.5 Wave-Guide....................................................................................................................................................................19
6.1.6 Curved antenna extensions ............................................................................................................................................20
6.1.7 Special options for the flange..........................................................................................................................................20
6.1.8 Ultimate installation on the tank......................................................................................................................................21
6.2 Ambient conditions..........................................................................................................................................................21
6.2.1 Hazardous locations........................................................................................................................................................21
6.2.2 Ambient temperature of signal converter........................................................................................................................21
6.2.3 Flange temperature.........................................................................................................................................................21
6.2.4 Ambient temperature limits .............................................................................................................................................22
6.2.5 Storage temperature.......................................................................................................................................................22
6.2.6 Environment class...........................................................................................................................................................22
6.2.7 Protection category.........................................................................................................................................................22
6.2.8 Shock resistance.............................................................................................................................................................22
6.2.9 Vibration endurance limit.................................................................................................................................................22
6.2.10 EMC................................................................................................................................................................................22
6.3 Product conditions...........................................................................................................................................................22
6.3.1 Physical properties of the products.................................................................................................................................22
6.3.2 Relative permittivity (εr≥1.5)..........................................................................................................................................23
6.3.3 Product limitations...........................................................................................................................................................23
6.3.4 Product temperature (unrestricted).................................................................................................................................23
6.3.5 Maximum allowable operating pressure..........................................................................................................................23
6.4 Maintenance....................................................................................................................................................................24

BM 70 M 3
7 Design............................................................................................................................................................................24
7.1 Dimensions and weights.................................................................................................................................................24
7.2 Replacement of the signal converter ..............................................................................................................................25
7.3 Field assembly................................................................................................................................................................26
7.4 Materials of construction.................................................................................................................................................26
7.4.1 Signal converter..............................................................................................................................................................26
7.4.2 Flange system.................................................................................................................................................................27
7.4.3 Seals and gaskets...........................................................................................................................................................27
7.5 Process connection.........................................................................................................................................................27
7.6 Electrical connection.......................................................................................................................................................28
7.7 Terminating resistor for the RS 485 interface.................................................................................................................30
8 User interface................................................................................................................................................................ 30
8.1 Local display...................................................................................................................................................................30
8.2 Function of the keys........................................................................................................................................................31
8.3 Operator control concept ................................................................................................................................................32
8.4 Table of settable functions (Versions 3.00, 3.01, 3.02, 3.03, 4.02, 4.03)........................................................................34
8.5 Configuration examples..................................................................................................................................................39
8.5.1 Level measurement (example) .......................................................................................................................................40
8.5.2 Volume measurement (example)....................................................................................................................................40
8.6 Description of functions...................................................................................................................................................41
8.6.1 Choice of units................................................................................................................................................................41
8.6.2 Vessel (tank) height........................................................................................................................................................43
8.6.3 Block distance, antenna type and antenna extension.....................................................................................................44
8.6.4 Distance piece ................................................................................................................................................................44
8.6.5 Stilling well......................................................................................................................................................................45
8.6.6 Reference and tank bottom offsets.................................................................................................................................45
8.6.7 Display............................................................................................................................................................................47
8.6.8 Current output I...............................................................................................................................................................48
8.6.9 Communication interfaces ..............................................................................................................................................49
8.6.10 Display............................................................................................................................................................................50
8.6.11 Auto tank height..............................................................................................................................................................51
8.6.12 Empty spectrum..............................................................................................................................................................51
8.6.13 Time constant and tracking speed..................................................................................................................................54
8.6.14 Multiple reflections and block distance detection............................................................................................................54
8.6.15 Tank bottom tracing system............................................................................................................................................55
8.6.16 Tank type, movement of product surface........................................................................................................................56
8.6.17 Switching output..............................................................................................................................................................56
8.7 Functional checks...........................................................................................................................................................59
8.7.1 Main menu 2.0 Test functions.........................................................................................................................................59
8.7.2 Hardware test..................................................................................................................................................................59
8.7.3 Test of current output......................................................................................................................................................60
8.7.4 Test of switching output..................................................................................................................................................61
8.7.5 Display of firmware version.............................................................................................................................................61
8.8 Pointers and error messages during measurement........................................................................................................61
8.8.1 Different kinds of messages............................................................................................................................................61
8.8.2 Pointers provided by 6 markers during measurement....................................................................................................62
8.8.3 Error messages and their representation in display and at outputs................................................................................63
8.8.4 Error display during measurement..................................................................................................................................64
8.8.5 Error list...........................................................................................................................................................................64
8.9 Messages on start-up .....................................................................................................................................................64
8.10 Faults and symptoms during start-up and measurement................................................................................................64
8.11 Calculation of the measured value..................................................................................................................................70
8.12 User program PC-CAT for Windows...............................................................................................................................70
9 Power supply.................................................................................................................................................................71
9.1 Options, technical data ...................................................................................................................................................71
9.2 Fuses..............................................................................................................................................................................72
9.3 Changeover of operating voltage and replacement of fuses ..........................................................................................72
9.4 Advice on safety..............................................................................................................................................................73
10 Certificates and approvals...........................................................................................................................................75
10.1 Declaration of Conformity ...............................................................................................................................................75
11 Ordering information....................................................................................................................................................76
12 External standards, codes and directives..................................................................................................................77
13 Quality assurance.........................................................................................................................................................77

4 BM 70 M
General advice on safety
Weight: the device will weigh between approx. 55 kg (120 lb) and 70 kg (155 lb)
or more!
To carry, use both hands to lift the device carefully by the converter housing. If
necessary, use lifting gear.
Avoid hard blows, jolts, knocks, impacts, etc.
Product liability and warranty
The BM 70 M level gauge is designed solely for measuring the distance, level, volume and
reflection of liquids, pastes, slurries, solids and particulate materials.
The BM 70 M level gauge does not form part of an overfill protection system as defined in WHG.
Special codes and regulations apply to its use in hazardous areas.
Responsibility as to suitability and intended use of these level gauges rests solely with the user.
Improper installation and operation of our level gauges may lead to loss of warranty.
In addition, the "General conditions of sale", forming the basis of the purchasing contract, are
applicable.
If you need to return the level gauge to the manufacturer or supplier, please refer to the
information given on page 86.
Items supplied
Depending on the version ordered we supply the following:
• Signal converter bolted to waveguide window and antenna
Optional: antenna extension, sunshade (with fastening material in each case)
• Report on factory settings for the signal converter
• Bar magnet for operator control / parameter assignment (only in version with local display)
• Wrench for the covers
• Installation material (stud bolts, flange gasket and cabling) not supplied, to be provided by
customer!
Documentation supplied
Condensed instructions: installation, connection, start-up and safety advice in condensed form,
but sufficient for most applications. Please read through these instructions first!
Instruction card: overview of the configuration menu and meaning of the markers in cheque card
format.
Installation and operating instructions (this manual): detailed user manual and reference book,
including description of special versions and functions. This documentation is structured on lines
similar to those given in the DIN V 19259 Standard.
Approval documents, unless reproduced in the installation and operating instructions.
Software history
Introduction
Mth./Yr Firmware version Device instructions Remarks
06/02 4.04 06/02 First serial version
06/02 4.06 06/02 Minor amendments

BM 70 M 5
1 Range of applications
The BM 70 M Level-Radar level gauging system is designed to measure the distance, level,
volume and reflection of liquids, pastes, slurries, solids and particulate materials.
BM 70 M Ex hazardous-duty versions are suitable for use in Ex-Zone 0, 1 and 2.
2 Mode of operation and system structure
2.1 Operating 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 transmits 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 corresponds 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 an 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.
An immediate frequency regulation is necessary with the BM 70 M 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.
3) differential frequency
formed 1) radar frequency
linearly changed
2) delay time due to wave
propagation
f∆f
t
antenna
∆f
non-linear sweep linear sweep
fStart
fStop

6 BM 70 M
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.
Microprocessor
control Reference oscillator
Phase
detector
Microwave
oscillator
Loop
filter
Antenna
PLL structure
2.2 Signal processing (digital)
The radar signals are digitally processed by a microprocessor. The processing system is based
on intelligent procedures that allow for plausibilities and history.
The following diagram describes the path of internal signal processing:
After automatic gain control, the measuring signal is filtered, digitized and converted into a
frequency spectrum by means of the Fourier transform. Plausibility of the value obtained is
assessed with the aid of the so-called empty-tank spectrum, which contains information about
constant interference reflectors. Interpolation of the spectrum helps to improve resolution of the
measured value.
OO
OO
VFourier
spectrum
interpolation
850.97:2
plausi-
bility
transform
filter analo
g
to
di
g
ital
spectrum
measurement
si
g
nal
g
ain
switch
g
ain
control
conversion corrected
empty tank spectrum
distanc
e

BM 70 M 7
2.3 Modularity (signal converter, flange, antenna)
The measuring system consists of the flange system and 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 standardised output signal (4 - 20 mA or digital interface).
The signal converter can be separated from the flange system under process conditions, without
loss of pressure or escape of product.
V96 version SA version
Converter
Flange
Antenna system
3 Input
3.1 Measured variable (distance, level, volume, reflection)
The primary measured variable 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.
3.2 Measuring range
Maximum tank height 0.5 m (20 inch)
Maximum measuring range 35 m (115 ft)
[0.5 - 35/40 m (1.64 - 115/131 ft)]
The useful range will depend on the antenna size, the reflection properties of the tank product,
the installation position, and the presence of interference reflectors (see Sections 6.1).

8 BM 70 M
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:
Horn antenna without stilling well Stilling well / Wave-Guide
The length of any antenna extension used must be
added on!
3.4 Out-of-range performance
When the level measuring range is exceeded (including flooding) the measured value will stick at
the (adjustable) block distance (see Sect. 8.6.14).
If the measured value drops below the level range, it will stay put at the set lower range limit
(distance = tank height).
4 Output
4.1 Variants
Variants Remarks 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 current output HART®intrinsically safe; passive; HART®protocol
(optionally with intrinsically safe switching output) 4.3 + 4.4
Current output Ex-e; active; non-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 -
All versions with HART®or BM70 protocols can be operated with the PC-CAT PC program (see
Section 8.12).
Product surface
Storage tanks: 10cm/4"; Process tanks: 20cm/8"
Antenna size* = Type3: 22cm/8.7"; Type4: 34cm/13";
* Hastelloy: +3cm / 1,2 "
Recommended antenna distance:
Product
Antenna size * = Type1: 11cm/4";
Type2: 15cm/5.5"; Type3: 22cm/8.7"
Recommended antenna distance =
30 cm / 12"
(Wave-Guide: no antenna)
* Hastelloy: 3 cm (0.4")
Wave-Stick SW: 6cm/2.4"
Maximum
level
Block
distance

BM 70 M 9
BM 70 A
HARTspecificsoftware
andoperating devices
Converter
HART-
HHC
HART Communicator
HART
FIELD COMMUNICATIONS
O
I>>>
F1 F2 F3 F4
A B C D E F G H
7 8 9
J K L M N O P Q
4 5 6
S T U V W X Y Z
/
1 2 3
# %& < >: +
0 . _
*
HART-Master TankInventory System
4 ... 20mA
+ HART ®
Modbus
PROFIBUS-PA
...........
Other
communication interfaces
RS 485
RS 485
4mA (Ex i)
+ HART®
PC-CAT
or
HART Communicator
HART
FIELD COMMUNICATIONS
O
I>>>
F1 F2 F3 F4
A B C D E F G H
7 8 9
J K L M N O P Q
4 5 6
S T U V W X Y Z
/
1 2 3
# %& < >: +
0 . _
*
HART-
HHC
Overview of digital Communication possibilities:
Point-to-point Multidrop
4.2 Ex-e current output HART®
Function Level, distance, volume (conversion table) or reflection, and error
identification; galvanically isolated from digital input and switching
output
Current 4-20 mA; without or with error message (2 mA and 22 mA)
Accuracy/linearity 0.05 % (rel. 20 mA; at T = 20°C, 100ohm load impedance and nominal
operating voltage)
Temperature drift < 100 ppm/K (typically 30 ppm/K)
Load impedance < 500 ohm
Effect of load
impedance < 0.02 % (rel. 20 mA for RB = 0...500 ohm)
Effect of power 0.02 % (rel. 20 mA for UB within 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 suspend the entire measurement procedure, i.e. measurements are "frozen"
(standard setting), or to hot start the device (reprogramming by KROHNE Service).
Applicable voltage 5...28 V DC
Input resistance > 1 kohm
Switching output (terminals 41/42):
Can be programmed as a limit switch, alarm contact or error message. The contact is open in the
de-energized condition.
Operating data max. 100 mA / 30 V DC or 30 V AC
Internal resistance < 20 ohm

10 BM 70 M
HART
Master 4...20 mA
4.3 Ex-i current output HART®(type of protection: Ex de [ia])
Function Level, distance, volume (conversion table) or reflection; and error
identification; passive output (current sink)
Current 4-20 mA; without or with error message (3.6 mA / 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, 10 V supply voltage and nominal
operating voltage)
Supply voltage U 8-30 V (between terminals 31 and 32)
Load impedance < (US - 8V) / 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 UB within limits of tolerance)
Note Digital input 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
deenergized condition.
Operating data 6...30 V; ILow < 110 mA; 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:
Uo= 30 V; Ik= 250 mA
Effective inner capacitance ≈0; effective inner inductance ≈0
4.4 HART®communication
The HART®Communications protocol can, in accordance with the Rosemount Standard, be used
with a BM 70 M.
Electrical connection: see Section 7.6.
There are two ways of using the HART®Communication:
Point-to-point connection Multipoint connection (Multidrop)
between the BM 70 M and the HART®
master equipment.
A BM 70 M can be used either with an
Ex-e current output HART®or with an
Ex-i current output HART®.
with up to 15 devices (BM 70 M or other HART®
equipment), in parallel on a 2-wire bus. A BM 70 M 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

BM 70 M 11
RS485 connection must
be terminated with 120 ohms
(if necessary insert resistor
between A and B
)
Computer
system Bus line (2 shielded wires)
with termination
resistance
120 ohms
4.5 Current output (non-communicable)
Function Level, distance, volume (conversion table) or reflection, and error
identification
Current 4-20 mA; without or with error message (2 mA and 22 mA)
Accuracy/linearity 0.3 % (rel. 20 mA; at T = 20°C, 100 Ohm load impedance and
nominal operating voltage)
Temperature drift < 200 ppm/K (typically 70 ppm/K)
Load impedance < 250 Ohm
Effect of load impedance < 0.1 % (rel. 20 mA for RB = 0...250 Ohm)
Effect of power < 0.1 % (rel. 20 mA for UB within limits of tolerance)
Hazardous-duty version Ex e
When operated as a switching output (digital output):
Function limit switch, alarm contact or error message
Low status current < 2 mA
High status current = 22 mA (when load < 250 Ohm)
No-load voltage < 18 V
4.6 Digital interface RS 485
RS 485 is a bus that allows two-way Communication (half-duplex operation) with the BM 70 M
Level-Radar. When the computer system sends out a request, the BM 70 M transmits: level,
distance; volume (conversion table), reflection, setting parameters and status.
A PC can configure any BM 70 M 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.
Transmission rate 1200 to 38400 bauds
Address 0 to 255
Protocols KROHNE Protocol, HART®, Modbus RTU (from firmware
V.3.02/4.02)
Additional information: see "BM 70 A/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 are not available.
However, the current output can be configured as a switching
output.
Various bus configurations
A) Connection of a BM 70 M as a single RS 485 user:

12 BM 70 M
B) Connection of several BM 70 M in the RS 485 bus system via stubs to the bus cable:
C) Connection of several BM 70 M in the RS 485 bus system, with bus cable looped through to
further field instruments:
• If other devices are operated together with the BM 70 M Level-Radar on one
bus, all devices must use the same Communications protocol (e.g. ModBus
devices of different makes or BM 70 M and MTM 70 with KROHNE
Protocol).
• When "HART®" is set as the protocol type, use only the protocol in keeping
with the "HART®Specification". The "Hardware Implementation RS 485"
does not conform to the HART®Standard (see Sections 4.2 and 4.3).
• 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 Ohm). To do this inside the BM 70 M: see Section 7.7.
4.7 Breakdown signal
Breakdown information can be called up via the following interfaces:
• Local display: flashing display, plain text information
• Current output: error signal 2 mA (Exi = 3.6 mA) or 22 mA
• Switching output: contact opens or closes
• Digital interfaces: interrogation of error flags
Computer
system
...........
RS485 connection must
be terminated with 120 ohms
(if necessary 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
...........
with termination
resistance
120 ohms
without
resistance
termination without
resistance
termination without
resistance
termination
Bus line (2 shielded wires)
Computer
system
RS485 connection must
be terminated with 120 ohms
(if necessary insert resistor
between A and B)

BM 70 M 13
4.8 Digital input
The digital input (for electrical data: see Section 4.2) can be used for temporarily "freezing"
measurements 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
agitator, slide gate, ball valve in the stilling well. The last measured values in each case are
present at outputs I and S, and in the display. The digital input is also taken into account when
the empty-tank spectrum is being recorded (totalizer does not continue). Marker 6 in the display
indicates that the digital input is active in the "freeze" function.
The function of the digital input is set as standard to "freeze". To switch the
function to "hot start" or to deactivate it completely, the setting will need to be
changed in the Service menu of the BM 70 M.
5 Measuring accuracy
5.1 Reference conditions
Temperature +20°C / +68°F
Pressure 1013 mbar abs. / 14.5 psia
Air humidity 65%
Highly reflecting product (e.g. water) with calm surface
Tank diameter > 5 m / 16.4 ft
Mounted at least 1/7 x tank height away from tank edge (BM 70 M: 1/5 x tank height)
No interference reflections inside the 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 figures given in this Section 5 refer to
the measured distance.
Only with antenna type 4 (200 mm / 7.87") or stilling well 100 - 200 mm dia. (4 - 8")
-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
Accuracy
1
Block-
distance
± 0.01 %
± 2 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

14 BM 70 M
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 0.1 mm / 0.004" for BM 70 M.
Hysteresis is at least 20 times less 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 approx. 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.
5.6 Long-term drift
The long-term drift is within the specified error of measurement.
5.7 Effect of ambient temperature
Temperature coefficient, signal output:
Ex-e current output HART®< 100 ppm/°C (typically: 30 ppm/°C)
Ex-i current output HART®< 100 ppm/°C (typically: 30 ppm/°C)
Current output < 200 ppm/°C (typically: 70 ppm/°C)
Digital interfaces no temperature effect
The temperature has no effect on the measured value as the device carries out a regular self-
calibration.
The temperature of the atmosphere above the liquid product results theoretically in -1 ppm/°C for
air.
When ascertaining temperature effects using reference measurements in liquid tanks, it needs to
be remembered that liquids generally have a high coefficient of expansion (organic liquids:
typically 0.15 %/°C)!
6 Operating conditions
Hazardous-duty systems:
• The BM 70 M is certified in conformity with European Standard (ATEX) for use in Zone 0, 1
and 2 hazardous locations.
• The BM 70 M also has FM Approval (Factory Mutual) for CLASS I, DIV 1, GROUPS B,C,D;
CLASS II/III, DIV 1, GROUPS E,F,G (in preparation)
• Attention is drawn to the information given on the nameplate and the specifications in the
approval certificates.
• When carrying out installation, dismantling work or making electrical connections in the
hazardous area, be sure to observe the pertinent wiring and installation regulations, e.g. as
specified in VDE 0165.
• Within the scope of routine checks required to be carried out on systems operated in
hazardous areas (maintaining the system in good working order), the "flameproof enclosure"
(large cover on signal converter) should also be visually inspected for signs of external
damage and corrosion.
• Before opening the "flameproof enclosure" (e.g. to inspect the inside or for repair purposes)
make absolutely certain in the hazardous location:
- that the BM 70 M Level-Radar is disconnected from voltage, and then allow the prescribed
waiting time of 22 minutes to elapse first,
- and that there is no explosion hazard (gas-free certificate!).

BM 70 M 15
D
>1/7×H, but max. 1/3×D
Antenna T
yp
e 3
or Wave-Stick
H
measurable
level
min.
Safety:
• Operator control via the keys: on electrical safety grounds, operator control of the keys (below
the display, with the housing open) may only be carried out by specialist personnel for service
and repair work, on no account, however, when there is risk of explosion!
• Surface temperature: the housing of the signal converter can, in extreme ambient conditions,
assume temperatures of more than 70°C (158°F)!
6.1 Installation conditions
6.1.1 Transmission angle
The transmission angle is defined as the angle .to the vertical, in which the power density of the
radar waves assumes half the value of the maximum power density (half-power beam width):
Antenna
Type Diameter mm
(inches)
Transmissi
on angle αLobe expansion s
per metre distance
Type 4 200 (7.87) 6° 10 cm (3.94”)
Type 3s* 140 (5.51) 8° 14 cm (5.51”)
Type 2s* 100 (3.94) 12° * 22 cm (8.67”)
Type 1s* 80 (3.15) 16° * 30 cm (11.8”)
Wave-Guide
/ stilling well 25-200 (0.98-7.87) Propagation only inside the stilling well
* Should only be used in stilling wells; the transmission angle given
applies to line-of-sight propagation, i.e. without stilling well.
6.1.2 Recommendations for positioning on the tank
A) Horn antenna or Wave-Stick without stilling well
Recommended distance from
the tank wall Lower measuring range limited when tank has tapered
bottom.
Several BM 70 M can be
operated in one tank.
αα
s

16 BM 70 M
Do not position in tank
centreline! (multiple
reflections!)
Do not mount dead centre on
manhole cover! (multiple
reflections!)
Do not position above
internals! (interference
reflections!)
If these recommendations cannot be followed because of the tank geometry, please consult
KROHNE.
B) Stilling well or Wave-Guide
A stilling well or Wave-Guide may be mounted in any position on the tank.
(For design layout: see also Section 6.1.4; for block distance: see Section 3.3).
Stilling well application

BM 70 M 17
6.1.3 Mounting on tank fitting
A) Horn antenna
Should be mounted on the tank fitting as close to the horizontal as possible (deviation < ± 2°).
Exception: if product surface is not horizontal, (e.g. particulate materials) the flange can be
aligned roughly parallel to it.
The antenna should project out of the fitting:
Antenna Diameter D Length l*
Type 4 200 mm (8”) 335 mm (13.2”)
Type 3 140 mm (5.5”) 223 mm (8.8”)
* Hastelloy: + 30 mm (1.2”)
(subject to change without notice)
An antenna extension should be added if the antenna does not project out of the fitting:
Antenna extensions are available from 100 to 2000 mm (3.94" to 78.74") in steps of 100 mm
(3.94"). Several extensions can be joined up.
Exception:
When the tank fitting is symmetrical, the antenna may end in the fitting so as 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
D
L
Tank nozzle Antenna
extension
Tank nozzle

18 BM 70 M
B) Solid antenna
6.1.4 Mounting on stilling wells/ trunks
Antenna Type Outside diameter
1s 76 mm (2.99”)
2s 100 mm (3.94”)
3 140 mm (5.51”)
3s 152 mm (5.98”)
4s 200 mm (7.87”)
If necessary, turn antenna to size!
Further requirements on stilling wells:
• The well must be electrically conductive.
• Minimum inside diameter of well: 40 mm (1.57"). (BM 70 M: 80 mm, better > 100 mm).
• If possible, use only smooth walled, straight stilling wells. If nevertheless an assembled stilling
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").
• For the BM 70 M the antenna types 1s, 2s, 3s or 4s have to be used to achieve a high
measuring accuracy.
It is possible to measure through a full-bore open ball valve if the valve and the pipe adapters
above and below the valve are relatively smooth-walled.
It is not possible to measure levels below the end of the stilling well.
To ensure equalization of pressure, drill one or two small holes in the stilling well above the
maximum filling level.
800 mm

BM 70 M 19
If necessary, several holes can be drilled along the whole length of the pipe. All holes must be
deburred. The holes should be as small as possible and spaced wide apart (Recommendation:
see drawing below).
It is advisable to fit a reference point at the end of the stilling well in the form of a rod or screw of
approx. 6 mm (0.24") diameter. See drawing below.
6.1.5 Wave-Guide
The "Wave-Guide" is a pipe with an outside diameter of 30 mm (1.18") and an inside diameter of
25 mm (0.98"), that is bolted direct to the BM 70 flange system (in the same way as an antenna
extension). It functions like a stilling well and can be used for clean products. The Wave-Guide is
not practical in conjunction with the BM 70 M as it will not provide high measuring accuracy.
Maximum length:
Ex: max. 3 m (9.84 ft) (except tantalum: max. 1 m (3.28 ft)).
Non-Ex: up to 3 m (9.84 ft) without additional support
Pipes longer than 3 m (9.84 ft) need to be fixed at two points.
Ø max.
10 mm
/
0.4’’
min.
50 mm / 1.97’’
6 mm Ø
Ø 0.24’’

20 BM 70 M
6.1.6 Curved antenna extensions
Rectangular and S-shaped extensions are available for particularly difficult operating conditions.
Such extensions can be used in cases where the antenna is exposed to especially high
temperatures and where there are problems of space, (e.g. to avoid internals; positioning the
antenna away from the centre of symmetry; lateral mounting of the signal converter).
Standard sizes (others on request):
Dimensions in mm (inches)
6.1.7 Special options for the flange
Antenna heating/cooling device
(> DN150/6") Purging device (> DN100)
Double-walled antenna for cooling or heating,
e.g. to avoid condensation (recommended for
liquid sulphur).
max. differential pressure at antenna:
Standard DN150 = 6 bar (87 psig)
(information on other pressure levels
provided on request)
With connection for purging the inside surface of
the antenna to prevent heavy deposits of product
or to heat or cool the antenna
271 (10.67")
R 110 (4.33")
271 (10.67")
271 (10.67")
300 (11.81")
323 (12.72")