Buffers are bond graph elements that can store energy. There are two types of buffers: C-elements and I-elements. The table below shows the effort and flow descriptions that belong to these elements. The parameters "C" and "I" are the bufferconstants, which determine a linear buffer behavior. Examples of C-elements are a mechanical spring and an electrical capacitor. Examples of an I-element are a mechanical inertia and an electrical inductance.
C-element |
bond graph element |
equation |
effort-in causality |
f = C de/dt |
|
effort-out causality |
e = (1/C) int(f) |
|
I-element |
bond graph element |
equation |
effort-in causality |
f = (1/I) int(e) |
|
effort-out causality |
e = I df/dt |
Buffer elements do not fix the direction of the effort and flow. Both effort-in as well as effort-out causality is allowed. With simulation however, we prefer to avoid differentiation. in other words, with the C-element the effort-out causality is preferred and with the I-element the effort-in causality is preferred.