Campbell Scientific CS420 and CS425 PDCR 1830-8388 Pressure Transducer - Manual (Page 9)

CS420-L and CS425-L Pressure Transducers
5.2.2 Calculating the Offset
The offset is calculated with the following procedure:
1. Program the datalogger using the calculated multiplier and an offset of 0
in either a 6-wire full bridge instruction (BrFull6W in CRBasic or
Instruction 9 in Edlog) or a 4-wire full bridge instruction (BrFull in
CRBasic or Instruction 6 in Edlog). Set the execution interval to one
second.
2. Install the Druck transducer and a staff gauge at the same location or
install the Druck transducer at a known depth.
3. If applicable, measure the depth using the staff gauge.
4. Use a keyboard display or PC to view the depth reading (refer to your
datalogger manual for information about viewing real-time data).
5. Subtract the value displayed on the keyboard display or PC from the
known depth or the staff gauge’s reading.
Always make sure your multiplier and offset are in the same
units (e.g., feet, inches). NOTE
When using Edlog, large offsets may cause truncation of Final
Storage values resulting in fewer significant digits. If this is a
problem, do the offset correction after the data is collected or use
Instruction 78 to store the data in the high resolution format.
Example:
A staff gauge and a Druck transducer are installed at the same location. If the
staff gauge reads 10.07 feet and the value displayed on your keyboard display
or PC is 10.56 feet, the offset for the Full Bridge Instruction is:
Offset = 10.07 ft - 10.56 ft
= -0.49 ft
Enter -0.49 for the offset parameter in the Full Bridge Instruction.
5.3 Fine Tuning the Excitation and Input Range
Choose a datalogger input range that is larger than the output from the sensor.
The voltage ranges and codes are listed in your datalogger manual, the
CRBasic help, or the Edlog help.
Typically 2500 mV excitation is used with CR800, CR850, CR1000, CR10(X),
CR510, or CR500 dataloggers; 5000 mV is used with CR3000, CR5000,
CR23X, and 21X dataloggers. To calculate the sensor output when a specific
excitation is applied, use one of the following equations:
output mV =
(pressure range psig) (sensitivity (mV/V)
(psig) (excitation V)
∗
∗
5