CALIBRATION AND INITIAL SETTING OF CAPILLARY TYPE LEVEL TRANSMITTER:
If we are using capillary type level transmitter like Rosemount 3051CD series,
We can follow simple initial setting as follows:
- Install the level transmitter to the flanges provided i.e. LP side of the transmitter to top flange and HP side of the transmitter to the lower flange
- Keep the transmitter open to the atmosphere i.e. LP and HP side vented to atmosphere
- Power up the transmitter, the reading which is shown in the transmitter which will be generally a negative reading like for example -300 mm WC is the LRV value and note down this value
- Now the URV value is simply LP tap to HP tap (or centre to centre of the two capillary flanges ) measurement multiplied by specific gravity of the liquid inside vessel added to the LRV value For example if HP to LP distance is 600 mm and specific gravity of liquid inside vessel is 0.89 then URV is calculated as follows URV=LRV+(600*0.87)= -300+(522)=222mm WC
- After setting LRV and URV close the HP vent (drain) point and LP vent point.
- Line up both HP and LP side, the reading showing in the LT will be the process level in percentage.
- Take the necessary permit to work, take override if necessary
- Isolate the process i.e. close both LP and HP side and vent the both to atmosphere, Now the reading in LT should show 0% if not trim the transmitter
- Make an arrangement like that of a manometer, or a PVC transparent tube through which we can see water, and connect this to the drain(vent) point of the transmitter, measure the tap to tap point of LP and HP side and mark the corresponding 0%,25%,50%,75% and 100% in the PVC tube
- Now fill the water up to 25% and note the reading in LT it should show 25% and 8 mA. Similarly fill for 50% and reading should be 12mA,75% for 16 mA and 100% water in PVC tube for 20 mA
- Do span trim if necessary after filling 100% water, but if error is below 5%,it is advisable to not disturb the transmitter
- After calibration box up the transmitter, close the vent plugs and line up both LP and HP side
N.B: it is important to note that if initial setting is done for specific gravity 0.87 in transmitter and you are calibrating with water there will be some minor difference in the reading observed