In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 48)

Parameter Description Equation
3 Level, depth L
M
= D(P
M
)
4 Level, top of casing
L
M
= L
R
– (D(P
M
)– D
R
)
5 Level, elevation L
M
= L
R
+ (D(P
M
) – D
R
)
6.3.5 Pressure Reference
Master software may optionally overwrite the pressure reference value recorded by the device
when the Level Reference register is written. This register can be written only when the sensor
is in the calibration mode. The probe will return exception 0x92 (invalid sensor mode) if an
attempt is made to write these registers when the calibration mode is off. Master software must
ensure that the pressure value is written in the currently selected units. This value shall be
converted to the appropriate units when the Pressure Units ID register is written.
6.4 Calibration Procedure—Pressure
1. Write the Calibration On command (0xE000) to the Sensor Command register.
Reading the pressure parameter in the calibration mode shall present the raw
pressure (P).
2. Automatic barometric pressure compensation must be set to the desired mode.
3. Instruct the user to place the pressure sensor in open air.
4. Read the pressure parameter P.
5. Write P as the new value of P
O
to the pressure offset register.
6. Write the Calibration Update command (0xE001) to the Sensor Command
register. The sensor sets the last user calibration date to the current date and
sets the next user calibration date to zero (none required).
7. Optionally, read the last user calibration time, add the next calibration interval,
and write the result to the next user calibration time register.
8. Write the Calibration Off command (0xE002) to the Sensor Command register to
place the sensor in normal operation.
6.5 Calibration Procedure—Level
1. Write the Calibration On command (0xE000) to the sensor command register.
2. Instruct the user to deploy the probe and to independently determine the
reference level (L
R
).
3. Reading the level parameter in the calibration mode shall present depth using the
current level configuration settings to assist the user in properly deploying the
device.
4. Write the new value of L
R
to the Level Reference register.
5. The sensor measures the current pressure P
M
(with offset correction) and stores
it as P
R
.
6. Optionally, the master device can overwrite the pressure reference register with a
calculated value.
7. Write the Calibration Update command (0xE001) to the Sensor Command
register. The sensor sets the Last User Calibration Date to the current date and
sets the Next User Calibration Date to zero (none required).
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