4.4.4Ultra Low Dielectric (ULD) Mode Configuration
Note: Use this method for very low dielectric solids only, when little or no usable signal can be obtained from the product surface. Use in solids measurement applications with 1.3 < DC < 2.0. If the DC is above this 2.0 value please contact the factory for application support. Special calibration of the Trim Points is required.
1.The dielectric constant of the material must be stable and below 2. If the dielectric constant is above 2 and the MT2000 cannot be operated reliably in the direct reflect mode; the ultra low dielectric mode of measurement may be used if the target at the end of the probe/cable can be detected reliably with the vessel full. We recom- mend viewing the target reflection with an oscilloscope with the vessel full to verify that the measurement can be made reliably.
2.A suitable target is required at the bottom end of the sensor probe/cable. A 3" minimum diameter centering disk with holes is suitable, but needs to be on the cable, above any weight.
3.Set the Threshold Level THV = 1.5 V and the Gain Setting GS = 2
4.Set BLK to reject any signal above the target. Estimate BLK based on length of the probe/cable. BLK = 170 + L
*3.8 (L in inches)
5.The following procedures assume that the MT2000 is set up with the factory standard trim values of zero at the top of the probe.
6.If the product dielectric constant is known, calculate the desired LRV (4 mA point) and URV (20 mA point) values with the following formula and example below:
I = indicated level on read out with factory standard trim (inches, ft, mm, cm or m)
H = actual or desired height above the target at the end of the probe/cable
L = length of probe/cable from the coupler to the target (same units as H)
DC = product dielectric constant
I = H * SQRT (DC) – H + L
Calculate I at the desired LRV and URV. Make sure that EUN (engineering units), with the exception of percentage (%), are set at the same units used in the calculation. Enter the desired LRV and URV using the Calibration Menu of the MT2000.
After the LRV and URV have been entered, change the engineering units to % so that the MT2000 display will indi- cate level relative to the vessel.
Example: Probe length (L) is 360” from the target to the coupler. The product dielectric is 1.4. Desired 4 mA point is 12” above the target (H=12”). Desired 20 mA point is 24” below the coupler (H=336”). See Fig- ure 4.5.
LRV = H * SQRT (DC) – H + L | URV = H * SQRT (DC) – H + L |
LRV = 12 * SQRT (1.4) – 12 + 360 | URV = 336 * SQRT (1.4) – 336 + 360 |
LRV = 362.20” | URV = 421.56” |
Set LRV and URV to these values, and then change EUN to %. If EUN are not changed to % the indicator on the MT2000 will indicate 362.20” at 4 mA and 421.56” at 20 mA.
If the product dielectric constant is not known, establish a known level in the vessel. The most accurate results will occur when the known level is as high a possible. Use the following formula to calculate the product dielectric con- stant:
I = indicated level on read out with factory standard trim (inches, ft, mm, cm or m)
H = actual or desired height above the target at the end of the probe/cable
L = length of probe/cable from the coupler to the target (same units as H)
DC = product dielectric constant
DC = ((I + H – L) / H)2
After determining DC go to the previous Step 6 above to complete the setup.
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