KROHNE BM 70 M - Manual (Page 10)

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; I
Low
< 110 mA; U
Low
< 2V; I
High
< 900 µA (U=30V) and I
High
= 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:
U
o
= 30 V; I
k
= 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