Okay - work around - waiting to be confirmed
It would be good to do the multi meter thing to confirm the following.....
1. I confirmed the terminal on one end (the rounded socket end) is terminal 5 and is the "spare" temperature resistor (RTD). The centre pin I also confirmed as the Earth post.
Then I confirmed it matched the 2.20kOhm output with the spec sheet and the temperature at the time of 22.7C. I formulated a plot for 10-50degC and worked out a reverse engineering formula (solution) that - given a kOhm output I can work out a degC.
2. I had a bit of think. I figured the HFM-5's* "may" all use the same element, and the element is simply influenced (as a very rough assumption) by the velocity through the throat/venturi.
So I analysed the kg/hr, worked out m3/s and then divided by the throat m2 to get m/s throat velocity. I then read off the Volts at 100, 300 and 48kg/hr for each of the 5 curves. Then I plotted velocity versus Volts output and voila....a reasonable fit.
I've attached my rough calc sheet - for anyone interested.
Measuring our throat at 60mm ID, I'm thinking we are closest to Curve 1, however it tails out at <400kg/hr and so I think that's why it has the 130mm length - to afford some more flow straightening.
Anyway - I'm going to move on and work with this until a better curve pops up. I'll hook up my spare to 14V battery and a pitot tube flow bench setup and see what comes out.
*(note - ours is called a HFM5-4.7 by maf-shop.com and I've emailed them for a chart)