KROHNE BM 102 Handbook - Manual (Page 21)

BM 102 21
Example for calculating the power supply:
The voltage drop is tested at 22 mA.
U
power min. 22
= 22 mA x load impedance + Uinput min. 22
U
power min. 22
= 22 mA x 250 ohms + 10 V = 5.5 V + 10 V = 15.5 V
In order to cover the whole current range, the voltage drop must also be tested at 4 mA.
By analogy, the following applies:
U
power min. 4
= 4 mA x load impedance + Uinput min. 4
U
power min. 4
= 4 mA x 250 ohms + 18 V = 1 V + 18 V = 19 V
At a load impedance of 250 ohms, a power supply voltage of 19 V is sufficient to energize the
current device range of 4 to 20 mA.
2.2.2 Hazardous-duty
version
The certified device may only be used with other ’Ex’ certified equipment. The minimum electrical
safety data indicated on the nameplate must be observed. To ensure proper operation, the
minimum parameters specified above in section 2.2.1 for the power supply must be observed to
ensure that a given 4 to 20 mA converter is adequate for use with the BM 102. Refer to the BM
102 MICROFLEX KEMA 00 ATEX 1101X Supplementary Installation and Operating Instructions
for further information. This document is available from the “Download Centre” on KROHNE’s
website http:// www.krohne.com/.
In addition, the connected
equipment must be HART
® -
compatible so that it can be
operated with the
communication software or
the HART
®
communicator.
An ’Ex’ repeater power
supply unit must be used.
For calculation of the supply
voltage the same applies as
for the non-’Ex’ version.