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:
Summary of Contents for BM 70 M Series
Page 75: ...BM 70 M 75 10 Certificates and approvals 10 1 Declaration of Conformity...
Page 83: ...BM 70 M 83 Annex C Spare parts...
Page 84: ...84 BM 70 M...
Page 85: ...BM 70 M 85...
Page 102: ...16 BM 70M EEx BM 70Mi EEx 11 Approvals...
Page 103: ...BM 70M EEx BM 70Mi EEx 17...
Page 104: ...18 BM 70M EEx BM 70Mi EEx...
Page 105: ...BM 70M EEx BM 70Mi EEx 19...
Page 106: ...20 BM 70M EEx BM 70Mi EEx...
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Page 108: ...22 BM 70M EEx BM 70Mi EEx...
