APG MNU IS Series, User Manual

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Appendix B: MNU IS Barrier Notes
Devices rated Intrinsically Safe for use in hazardous locations require the use of barriers to limit the total
amount of electrical and thermal energy present in the device and circuit within the the hazardous area.
The allowable limits--called entity parameters--for the MNU IS, as determined by CSA, are listed on drawing
9005002.
Barriers for Modbus devices are more difficult to deal with than 4-20 mA devices, as the limits are stated in
total but must account for both the supply voltage and the communication signal. This can be accomplished
with one barrier or two.
Below is an example of using two barriers, and their resultant entity parameters, which together meet CSA’s
requirements for use with the MNU IS.
• IS Barrier Notes
24 VDC Barrier (APG P/N 200187)
Line
Barrier Specifications
Entity Parameter Requirements
Voltage Rmin Rmax Imax Vmax Imax Pmax Lmax Cmax
V+ 24 VDC 241 Ω 252 Ω 100 mA 28 VDC 119 mA 833 mW 0.228 μH --
RS-485 Barrier (APG P/N 200186)
Line
Barrier Specifications
Entity Parameter Requirements
Voltage Rmin Rmax Imax Vmax Imax Pmax Lmax Cmax
TX+
9 VDC 1043 Ω 1156 Ω 7.7 mA 12 VDC 12 mA 40 mW 850 μH 9 μF
TX-
9 VDC 1043 Ω 1156 Ω 7.7 mA 12 VDC 12 mA 40 mW 850 μH 9 μF
Total
18 VDC -- -- -- 24 VDC 24 mA 80 mW 145 μH 0.93 μF

IMPORTANT : To meet Intrinsically Safe installation requirements, barrier(s) used must
meet “Associated Apparatus with Entity Parameters” shown in drawing 9005002.

IMPORTANT : Case ground of IS barrier(s) must be connected to Equipment Ground
on supply side.