The sensors that can be used with this board all contain signal conditioning and temperature compensation. The final calibration of a system using the SX-10506 must be done as part of the application set up. As an example, say we wish to measure the height of water in a tank to a maximum height of 8 metres. Using an SX10506 loaded with a 14.5 PSI (100kPa, 10 metres H20) sensor, we need to calibrate the system to so that the sensing system reads zero when there is no water and 1 metre when the water head is at a height of 1 metre.

To do this, we need to take a reading with no water present (Poffset). This becomes the offset of the system. Then we take a reading with 1 metre of water (Pcal_1m). The span of the pressure measurement system is Pcal_1m – Poffset for 1 metre of water. The pressure for a given sensor reading is then:

Water height = (PressureSensorReading – Poffset) / (Pcal_1m – Poffset)

If during calibration, the reading with no water was 0.1107 (Poffset) and the reading with 1 metre of water was 0.1956 Pcal_1m, then a sensor reading of 0.6334 would give a water height of:

(0.6334 – 0.1107) / (0.1956 – 0.1107) = 6.16 metres

In practice it is always better to calibrate the system at the maximum pressure (more span), but this is not always practical. If we did calibrate at 8 metres, the equation would look like this:

Water height = (PressureSensorReading – Poffset) / ((Pcal_8m – Poffset) / 8)

Typically in your application program, Pcal and Poffset would be stored in non volatile memory once the calibration procedure had been done. Typically this procedure would be

1. Some key sequence to get the controller into the mode for pressure calibration
2. With no pressure (or water) press a button – controller notes the reading Poffset
3. Pressurise to some level and note the Pcal reading.
4. Save these parameters to non volatile memory

By knowing what height of water or pressure was used during the calibration procedure, the above equation can be used.