Intrinsically Safe Power Supply Connection - GasTech D-Guard2 Operator's Manual

9.4.2

Intrinsically Safe Power Supply Connection

Typically in an underground coal mining type application, a Group I certified
intrinsically safe power supply (isPSU) or intrinsically safe UPS (isUPS) would
be used rather than isolation barriers.
This allows multiple detectors (and other equipment) to be powered from a
single safe power source rather than multiple individual barriers.
Intrinsically safe power supplies are capable of supplying significantly more
power than an isolation barrier and therefore extreme care must be taken
in ensuring that only D-Guard
are connected to power supplies of this type.
Intrinsically Safe Group I certified power supply
It is critical that the power supply output parameters
are checked for suitability for connection to D-Guard
Typically the following parameters need to be considered.
U (maximum voltage appearing on the output terminal).
o
I (maximum current that the supply can provide).
o
C (maximum total capacitance the voltage output can safely drive).
o
L (maximum total inductance the voltage output can safely drive).
o
A typical intrinsically safe power supply (Austdac AC36W), may have entity parameters such as:-
U = 16V , I = 1.0A, C = 6uF, L
o o o
These must be compared to the entity parameter limits for the connected equipment (D-Guard
U = 22V (Group I certified variant).
i
I = 105mA (D-Guard 2 is internally fuse/resistor limited)
i
C = 0 (D-Guard has a capacitance value of zero appearing at its input terminals).
i
L = 0 (D-Guard has an inductance value of zero appearing at its input terminals).
i
Making the comparison between PSU and D-Guard
U = 16V U = 22V
o i
I = 1.0A I = 105mA
o i
C = 6uF C = 0
o i
L = 33uH L = 0
o i
Because the current loop output (power supply negative) terminal of the D-Guard
to the input voltage supply. Any connected equipment's input channel entity parameter for Ui, would need to
accommodate this voltage safely within its certified limit (e.g. U
The considerations for a Group II application using a suitably certified intrinsically safe power supply or barrier
are essentially identical to those above. For a Group II application, the voltages, current and power values in
question would differ, nonetheless, the process of entity parameter checking would follow the same process.
2
types carrying the appropriate certification
Safe area
2
.
= 33uH
o
2
will indicate whether safe connection is possible.
(which makes it compatible with D-Guard
2
(Ok since D-Guard is internally limited by fuse/resistor protection).
2
(D-Guard has no capacitance at its input so this parameter is ok).
(D-Guard 2 has no inductance at its input so this parameter is ok).
18
Sensor Controller
Hazardous area
2
).
2
could reach a voltage equal
= 16.5V).
i
2
D-Guard
2
).