Emerson Rosemount 975MR, Reference Manual

Page: 49 / 74

Table A-3: Contact Ratings
(continued)
Relay name Type Normal position Maximum
ratings
Auxiliary SPST N.O. 2 A at 30 Vdc
Fault (see notes 1
and 2) SPST N.C. or N.O. 2 A at 30 Vdc
1. The fault relay (in output configurations 1A, 2A, and 1R) is
normally energized closed during normal operation of the
detector. The relay is de-energized open if a fault condition or low
voltage situation occurs.
2. In output configurations 3A and 2R, the relay is normally energized
open during normal operation of the detector. The relay is de-
energized closed contact if a fault condition or low voltage
situation occurs.
• 0-20 mA current output: The 0-20 mA can be Sink or Source according to
the output configuration (see
General instructions for electrical wiring ) .
The maximum permitted load resistance is 600 Ω.
Table A-4: 20 mA Current Output
State Output
Fault 0 + 1 mA
BIT fault 2 mA ± 10%
Normal 4 mA ± 10%
Warning 16 mA ± 5%
Alarm 20 mA ± 5%
• HART protocol: The HART protocol is a digital communication signal at a
low level on top of the 0-20mA. This is a bi-directional field
communication protocol used to communicate between intelligent field
instruments and the host system. HART is available in output
configurations 1A, 2A, and 3A.
Through the HART protocol, the detector can:
— Display setup
— Reconfigure the setup
— Display detector status and definition
— Perform detector diagnostics
— Troubleshoot
For more details, refer to HART Manual 00809-0200-4975 .
• Communication network: The detector is equipped with an RS-485
communication link that can be used in installations with computerized
controllers.
Reference Manual Specifications and reference data
00809-0100-4975 August 2019
Rosemount 975MR 49