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Reference state: two property tables, one hidden offset

Subtract two states inside one table and the reference point cancels. Mix two tables and it does not. Check whether your sources differ by a constant before you trust a difference.

Live result

The two changes are 40000.000 and 40000.000 J/kg. A constant offset cancels.
The two changes are 40000.000 and 40000.000 J/kg. A constant offset cancels.

Two sources across two states

Two sources across two statesSource A runs from 100000.000 to 140000.000 and Source B from 400000.000 to 440000.000, both in J/kg. The offset is 300000.000 at the first state and 300000.000 at the second, so the offset drift is 0.000.Source ASource B

Try a record

50kJ/kg

Slide it and the two changes hold while both offsets move together.

Edit the two property records
Source A
Source B

Constant offset sensitivity

Shifted Source B record

The reported changes stay fixed when the same constant is added to both Source B states.

Entered record

40000.000 J/kg

Shifted Source B record

40000.000 J/kg

Authoritative result table

State 1 value
Source A
100000.000
Source B
400000.000
Difference
300000.000
State 2 value
Source A
140000.000
Source B
440000.000
Difference
300000.000
Change from state 1 to state 2
Source A
40000.000
Source B
40000.000
Difference
0.000
Offset at state 1
300000.000
Offset at state 2
300000.000
Offset drift residual
0.000

Equation trace, boundary, sources, and version

Equation trace

  1. Convert both sources to the canonical unit.
  2. Subtract state 1 from state 2 within Source A.
  3. Subtract state 1 from state 2 within Source B.
  4. Calculate the Source B minus Source A offset at each state.
  5. Subtract the two offsets and reconcile that result with the difference between the two changes.
ΔA=A2−A1\Delta A=A_2-A_1
where ΔA\Delta A is the Source A change, A2A_2 its second state, and A1A_1 its first state.
ΔB=B2−B1\Delta B=B_2-B_1
where ΔB\Delta B is the Source B change, B2B_2 its second state, and B1B_1 its first state.
d1=B1−A1d2=B2−A2d_1=B_1-A_1\qquad d_2=B_2-A_2d1=B1−A1d2=B2−A2\begin{gathered}d_1=B_1-A_1 \\ d_2=B_2-A_2\end{gathered}
where d1d_1 is the first state offset and d2d_2 the second state offset.
d2−d1=ΔB−ΔAd_2-d_1=\Delta B-\Delta A

Boundary

This comparison is valid only for the same property at the same two physical states and on compatible bases, and it does not reconcile different phases, compositions or state definitions.

Source anchors

Calculation version

1.0.0

The whole record prints. Your browser can save it as a PDF instead of printing it.

This page compares entered property values. It does not establish that the two sources describe identical physical states.

Related

Reference state cancellation record

Reference state: two property tables, one hidden offset

Accepted inputs

Property
Enthalpy
Source A State 1
100 kJ/kg
Source A State 2
140 kJ/kg
Source B State 1
350 kJ/kg
Source B State 2
390 kJ/kg
Constant added to both Source B states
50

Authoritative results

Source A Change from state 1 to state 2
40000.000 J/kg
Source B Change from state 1 to state 2
40000.000 J/kg
Offset at state 1
300000.000 J/kg
Offset at state 2
300000.000 J/kg
Offset drift residual
0.000 J/kg
Constant offset sensitivity
The reported changes stay fixed when the same constant is added to both Source B states.

Record fields

Calculation version
1.0.0
Boundary
This comparison is valid only for the same property at the same two physical states and on compatible bases, and it does not reconcile different phases, compositions or state definitions.
Ordered calculation trace
Convert both sources to the canonical unit. Subtract state 1 from state 2 within Source A. Subtract state 1 from state 2 within Source B. Calculate the Source B minus Source A offset at each state. Subtract the two offsets and reconcile that result with the difference between the two changes.
Source anchors
NIST REFPROP documentation; NIST REFPROP user guide

This page compares entered property values. It does not establish that the two sources describe identical physical states.

Calculation version: 1.0.0

Badr Alghamdi · badralghamdi.com/tools/reference-state-cancellation