Converting 0-100% into litres/second.

[PacoUmea]

Hi
New to all this and trying to convert a 0-100% value that i recive from VAV modules in building and converting these to litres/second. I know that 0% is the same as 20 litres/s and 100% equals 140 litres/second in this case. I tried to get som help from chatGPT and from this forum and others but there is somthing thats not working.
I got the following from the error log.

User script 13: attempt to perform arithmetic on local 'percentage' (a boolean value) stack traceback:
User script 13: in function 'convertFlowRate'

Code:

-- KNX group addresses
local PERCENTAGE_GROUP = "0/3/67"
local LITERS_PER_SECOND_GROUP = "0/3/68"

-- Flow rate conversion function
function convertFlowRate(percentage)
    local minPercentage = 0
    local maxPercentage = 100
    local minLitersPerSecond = 20
    local maxLitersPerSecond = 140

    -- Calculate the percentage within the range 0-1
    local normalizedPercentage = (percentage - minPercentage) / (maxPercentage - minPercentage)

    -- Calculate the flow rate within the range minLitersPerSecond-maxLitersPerSecond
    local flowRate = minLitersPerSecond + normalizedPercentage * (maxLitersPerSecond - minLitersPerSecond)

    return flowRate
end


-- Read the percentage from group 0/3/67
local percentage = grp.read(PERCENTAGE_GROUP)

-- Convert the percentage to liters per second
local litersPerSecond = convertFlowRate(percentage)

-- Write the liters per second to group 0/3/68
grp.write(LITERS_PER_SECOND_GROUP, litersPerSecond)

[admin]

You need to use event.getvalue(). grp.read() sends read request but does not return the actual value.

Code:

value = event.getvalue()
value = 20 + value * 1.2
grp.checkwrite('0/3/68', value)

[PacoUmea]

You need to use event.getvalue(). grp.read() sends read request but does not return the actual value.

Code:

value = event.getvalue()
value = 20 + value * 1.2
grp.checkwrite('0/3/68', value)

Ah, super! Thank you very much!