What is Simple Apparatus

Published 7 Oct '19
Read Time: 5 mins

AS/NZS 60079.11 – 2011 Definition

AS/NZS 60079.11 defines Simple Apparatus as follows:

3.1.5
simple apparatus electrical component or combination of components of simple construction with well-defined electrical parameters and which is compatible with the intrinsic safety of the circuit in which it is used

and further amplifies this in Clause 5.7:

5.7 Simple apparatus

The following shall be considered to be simple apparatus:
a) passive components, for example switches, junction boxes, resistors and simple semiconductor devices;
b) sources of stored energy consisting of single components in simple circuits with welldefined parameters, for example capacitors or inductors, whose values shall be considered when determining the overall safety of the system;
c) sources of generated energy, for example thermocouples and photocells, which do not generate more than 1,5 V, 100 mA and 25 mW.

But see the following notes:

NOTE 1 Sensors which utilize catalytic reaction or other electro-chemical mechanisms are not normally simple apparatus. Specialist advice on their application should be sought.
NOTE 2 It is not a requirement of this standard that the conformity of the manufacturer’s specification of the simple apparatus needs to be verified.

Examples of Simple Apparatus

The following common items fall into the category of Simple Apparatus:

• Thermocouples
• RTDs
• Strain Gauges
• Switches (limit, reed, magnetic, etc)
• Potentiometers
• Some semiconductors (for example, diodes)

Does Simple Apparatus have to be Certified?

The short answer to this is NO. However, where there is thought to be potential confusion or a great many of a device are to be manufactured, Simple Apparatus devices can be certified by a third party (an accredited certifying body under various schemes. Example: PTB under the ATEX scheme.)

Does Simple Apparatus have Entity Parameters?

The answer is generally no, but possibly none the less. Refer to AS/NZS 60079.11 Clause 5.2 (b):

b) sources of stored energy consisting of single components in simple circuits with well defined parameters, for example capacitors or inductors, whose values shall be considered when determining the overall safety of the system;

Inductance and Capacitance (including contributions from the connecting cable) still have to be considered. Co and Lo values may exist in the nF and μH range. It is always best to consult the Original Equipment Manufacturer directly with such questions.

In theory, a small network of inductance, resistance and capacitance could be placed with (say) a thermocouple to reduce induced electrical noise. The values of this passive filter – which is Simple Apparatus by definition – must be considered when calculating the compatibility of the connected intrinsically safe devices output entity parameters (Co, Lo).

Don’t forget the Cable

While the Simple Apparatus may have no discernible Capacitance or Inductance, the connecting cable will. Don’t forget to consider that cable capacitance and inductance.

This material is produced by HAZ. The information is of a general nature only and should not be relied upon.  Each set of circumstances associated with compliance of hazardous areas and Type B compliance is unique and expert advice on your particular circumstances should be sought.  HAZ accepts no liability for any reliance on the information published on this website.