Types of inputs for Trend IQ151+

I am looking at some problems we are having with our Building Management system (which consists of a number of Trend IQ151+
outstsaions, its about 13 years old)
I have a presure measurement sensor which is meant to be maeasuring supply duct pressure (for a control loop with the supply fan...) it appears to be giving negetive readings to the trend controller (i.e. a negetive voltage on the i/p pin, and more negetive as pressure increases so the output scale is 0 to -10V) should the inputs give intelligable values for this?
Does anyone know (or have the manuals for) what the range of possible input values that is acceptable for the ISS 3 input boards?
I hope someone out there might be able to help!
I can be contacted either on this email, or will check the board,
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