Intrinsic Safety Calculation query


I am checking some Intrinsic safe calculation. The instrument is a 3 wire
I.S. Device
device requiring 24VDC power and it acts as the current source for the 4-20mA signal back to the ICSS. The 24VDC power source for the device is fed through an I.S. Barrier to the device. The device acts as a current source for the 4-20mA I.S. signal and is connected back to the control system through a barrier.

1. Are two I.S. Calcs required - one for the power supply to the Instrument and the second one for the 4-20mA signal to the control system ?

2. Also, when comparing the Entity parameters in the first calc - it is straight forward as in the Entity Parameters (Output) of the barrier feeding the 24VDC is compared to the Device's (Max Input) entity parameters and ensure the I.S. criteria is met. What about the second calc - for the 4-20mA signal to the control systems' Barrier - Does the device's Uo, Io, Po parameters require to be compared to the control systems' barrier Ui, Ii and Pi parameters and additionally, for the Co and Lo - is it the device's Co and Lo to be used to meet the energy storage condition i.e, Ci (Barrier capacitance)+Cc should be less than Co (device capacitance) and Li (Barrier Inductance) +Lc should be less than Lo (Device Inductance) ? Or is the approach comparing the 24VDC Power barrier's Co and Lo with the Ci and Li of the Device and the 4-20mA signal's barrier

Hope this makes sense

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