# LH 2.4 AMM Parameters

This page contains paramaters relating to the AMM in LH 2.4

## AMM Linearization Map

Data Type: 8-bit integer, multiplied to 12-bit result
Range: Input is 0-255, lookup is 0-4095
Structure: 1x256 List

This list is used to convert the the raw ADC value from the AMM to an air mass value. In TunerPro it is usually represented as a 16x16 table for enhanced visibility.

There are three sections in this list. The first section is used as-is, the second is multiplied by 4, and the third is multiplied by 16. The 'Changeover Points' (below) establish where in the AMM list these points happen.

AMM Linerazation function (constants) for 016 AMMs:

This way the result is a 12 bit value between 0 and 4080 which represents the air mass flow.

Theory: Given that the 012 AMM maxes out at 680 kg/hour, each 'point' on the AMM scale equals about 2.8 grams/minute.

680 kg/hour = 680,000 grams/hour
680,000 grams/hour / 60 = 1133.33 grams/minute
1133.33 grams/minute / 4096 units = 2.7669 grams/minute per unit

This assumes that the 012 AMM hits 255 on the ADC scale at exactly 680 kg/hour, which is probably off by a bit. So, 2.5 grams/minute is probably closer (and a lot easier!)
-beepee

## Changeover Points

The changeover points are where in the linearization map sections two and three begin. The simplified process for reading the AMM is as follows:

1. AMM linearization table's location is loaded into register
2. AMM ADC value is read (0-255)
3. Value is read from (Table Location) + (ADC Value) and stored
4. ADC value is checked against second changeover point (AMM Table Location + 257). If the ADC value is greater than the second changeover point, the table value is multiplied by 16 and used as the result.
5. If ADC value is less than second changeover point and greater than first changeover point, the value in the table is multiplied by 4 and used as the result.
6. If ADC value is less than the first changeover point, it is used as-is.

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