Compound Units

Units may have powers applied by immediately appending an integer power. This is often the only way of inputting the units of some values. Limited alternative verbose forms are supported using additional words square and cubic (which can be abbreviated down to SQU and CUB). For example:

25ft2

25 square feet

300cm3

300 cubic centimetres

However the verbose syntax will not work with all abbreviations of standard units.

For compound units requiring more than one unit these should be appended either using a dot (.) or a slash (/) which inverts the following power. Density, Speed and Moments can be input using forms such as:

300kg/m3

55mile.hr-1

100newton.metre

Again limited verbose forms are also supported using either concentrated units or the additional word 'per' as in

55 lb per cubic foot

60 mile per hour

100 newton metre

However whenever values are reported back the verbose forms are generally NOT used.

Note:
The limitation below is not applicable to AVEVA Administration 1.8, AVEVA Engineering 15.3 and higher.

In general there is no serious limit to the complexity of compound units that may be entered.

However when compound units are stored by the system, in particular when setting current working units or setting Programmable Macro Language (PML) variables, there are limitations to the complexity of compound units that can be maintained.

No more than 4 component units can be used.

Each component unit can have:

• The named unit itself

• An optional power of the unit (multiple and/or reciprocal)

• An optional SI Prefix

When there is only one component it can be one of:

• Any standard unit

• -8>power>+8

• SI Prefixes femto to Exa

If there are two components these are defined with:

• Any standard unit

• -8>power>+8

• SI Prefixes femto to Exa for first component, and milli to Mega for second

If there are three components these are defined with:

• Any standard unit for first components, limited to 64 common units for last

• -8>power>+8

• NO SI Prefixes

If there are four components these are defined with:

• Limited to a set of 32 common units

• -2>power>+2 except the last unit which has power range of +/-4

• NO SI Prefixes

When the choice of units, powers or prefixes are restricted, the order of components may be adjusted to match a compound unit in range.