Appendix A: Safety Instructions – Ver. 1.00
31
Intrinsically safe I/O terminals for RHM:
RHM connections
Circuit name Terminals Uo [V] Io [mA] Po [mW] Lo [mH] Co [nF]
Drive circuit
1 - 2
8.1
136
275
1.9*
2000
Temp. sense
3-4, 5-4
6.1
45.7** 69.7
1
2000
Pickup circuit 6-7, 9-8
2.4
9
5.4
100
2000
*) 7.5mH for sensors RHM certified for gas group IIB / group C and D.
**) PtP (Terminal 3) and PtT (Terminal 5) share a common ground PtG (terminal 4) The maximum
current on terminal 4 therefor is 91.4mA.
Analog 4-20mA input
Circuit name
Terminals Uo [V] Io [mA] Po [mW] Li [mH] Co [nF]
Current Input 60 - 61
24.7
91.5
565
4.0
100
A.4
Thermal Safety Limits
The RHE26 and RHE27 must be installed in the safe area, therefor no temperature class is
specified for these units.
The ambient temperature must under no circumstances exceed the limits specified in chapter
A.10.
A.5
Grounding and Shielding
The RHE26/27 must be grounded.
The minimum cross section of the ground wire is 2.5mm². Wires with 2.5mm² can be connected
to the PE terminal 22 or to the M4 screw type terminal (only housing E*). Wires with a bigger
cross section must be connected to the M4 screw type terminal (only housing E*).
Shield between RHM and RHE:
IEC60079-0 recommends to ground shielded cables just on one end, normally outside the
hazardous area. On the other side the shield may be grounded via a 1nF capacitor.
In small installations (cable length typically less than 10m) the shield can be grounded on both
sides, provided that there is no potential difference between PE at the RHM and PE at the RHE.
This can be assumed if there is a good metallic contact or if a dedicated PE cable of at least 4mm²
connects the two grounding points.
Most RHM provide a PE terminal and terminal for grounding via 1nF. If there is no capacitive
ground, special measures might be required.
Power supply and I/O circuits:
I/O and supply cables should be shielded when fed outside the control cabinet. When unshielded
wires are used outside a building, dedicated surge suppressors must be used.
