Honeywell Enraf VITO, Instruction Manual

Page: 46 / 52

Appendix
___________________________________________________________________________
Instruction manual VITO Page 44
Appendix B Configuration procedure for 765/766/768 VITO water probe
Make sure the VITO water (and temperature) probe is installed properly (refer to installation guide VITO).
The test certificate, supplied with the probe, contains factory values for the minimum capacitance (probe in air)
and the maximum capacitance (probe in water).
The measured capacitance depends on the dielectric properties of the product. The dielectric constant for air is 1.
A general value for the dielectric constant of oil products is in the area of 1.8 – 2.5. For a 0.5 m (1’ 7”
11
/
16
) long
water probe that results in a change in minimum capacitance of 3 – 6 pF, which will cause 5 – 9 mm (
3
/
16
–
6
/
16
)
water level deviation. Therefore, the value for the minimum capacitance must be determined when the probe is
installed and completely, or partly, covered by product.
In the following 3 situations the water probe can be calibrated:
1. Some product in the tank (probe partly covered with product and partly covered by air)
2. Product in the tank (probe fully covered with product and no water)
3. Product and water in the tank (probe partly covered by water and partly covered by product)
In all other situations, no calibration can be made and the values from the test certificate shall be used.
Situation 1 (probe partly covered by product)
Refer to the figure: Manual measurement of water level, but read for the water level:
product level and read for
the product: air .
In items VR and VT must be entered the values from the “CheckList 765/766/768 Final Assembly”.
Measure the product level and calculate the immersed part of the probe.
Read the measured capacitance by item
MX
.
Then, the value for VR can be calculated as follows:
VR
cal.
represents the value from VR listed on the “CheckList 765/766/768 Final Assembly”.
Enter the value from VR
new
into item VR .
For example:
VR
cal
= 120.0 pF
VT = 430.4 pF
MX = 120.786 pF
WP = 0.485 m (or 19.09 inch or 1.591 ft)
WB = 0.025 m (or 0.98 inch or 0.082 ft)
Product level (measured by manual dip) = 0.122 m (or 4.80 inch or 0.400 ft)
Step 1:
Immersed part of probe becomes:
0.122 – 0.025 = 0.097 m (or 4.80 – 0.98 = 3.82 inch or 0.400 – 0.082 = 0.318 ft)
Step 2:
calculate value for VR
new