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manual abstract
The DB1 Liquid Level System requires a compressed gas supply. The most common gas is a 225 ft3 nitrogen bottle with an appropriate "automatic pressure relieved" pressure regulator. The pressure range set on the regulator depends on the water level to be recorded. For example, if the DB1 system is installed in a stilling well to measure stream level, and the stream level fluctuates between 5 and 15 ft (2.2 and 6.5 psi), set the pressure regulator above 7 psi (read 10 psi) to ensure adequate pressure. Open the nitrogen bottle valve, set the pressure regulator, and adjust the nitrogen flow by adjusting the two needle valves. The suggested bubble rate is 1 to 3 bubbles/seconds. The nitrogen gas bottle, regulator, and tubing (Campbell P/N 7567) are available from any welding supply store. Use common sense when installing pressure lines, checking for leaks, moisture, kinks, etc. in the lines. The DB1 does not have a mechanism to stop the flow of gas through the two submerged tubes so gas will be flowing constantly. This is very effective in reducing the growth of biomass in the tubes, which could otherwise reduce or block the flow of gas. If you wish to conserve gas, you can install a 12 Vdc solenoid valve between the gas bottle and the DB1 manifold and use the SW12V port on the datalogger to open the valve just prior to a measurement. This will result in slower consumption of nitrogen but may result in biomass build-up in the mouth of the tubes. 4. Wiring Wiring connections for the CR800, CR850, CR1000, and CR10(X) dataloggers are shown in Figure 3. The channel numbering in the wiring diagram matches the channel usage in the program examples. The pressure transducer within the DB1 has four conductors (white, green, red, black). The white lead connects to the high side and the green lead connects the low side of any analog channel (e.g. 1H and 1L). The red lead connects to any excitation channel and the black lead connects to any analog ground channel. The three relay cable assemblies have three conductors for each valve. The green wires connect to control ports C1 (Valve #1), C2 (Valve #2), and C3 (Valve #3) as used in the program example that follow. The red wires connect to 12 volts, and the black wires connect to ground. The cable assemblies have been provided with extra lead length to enable the user to cut the cables to length to accommodate different size enclosures. FIGURES 1 and 2. The DB1 System FIGURE 3. Wiring Diagram for DB1 CR1000, CR800CR850, 21X 5. Programming Every 60 seconds, the following program examples calculate the pressure transducer multiplier, measure the offset, and measure the liquid level. The average liquid level is stored in final memory every 15 minutes. 5.1 CR1000 Example 'CRBasic code for CR1000, CR800, or CR850 Public WtrLvl Public Batt_Volt Dim i Dim j Dim mv Dim Sum Dim Mult Dim Offset Dim Valve(3) Dim Delta_mV Const Delta_H = 'Set Delta_H equal to the vertical difference between the upper tube and lower tube. 'Unit of measurement of Delta_H will determine unit of measurement of final output. '\\\\\\\\\\\\\\\\\\\\\\\\ OUTPUT SECTION //////////////////////// DataTable(Table1,true,-1 DataInterval(0,5,Min,10) Sample (1,WtrLvl,FP2) EndTable DataTable(Table2,true,-1) DataInterval(0,1440,min,10) Minimum(1,Batt_Volt,FP2,False,True) EndTable '\\\\\\\\\\\\\\\\\\\\\\\\\\\ PROGRAM //////////////////////////// BeginProg Scan(5,Min, 3, 0) Battery(Batt_Volt) For i = 1 To 3 Select Case i Case 1 PortSet(1,1) 'Open valve to lower tube Case 2 PortSet(2,1) 'Open valve to upper tube Case 3 PortSet(3,1) 'Open valve to atmosphere EndSelect Delay(0,150,MSEC) Sum = 0 For j = 1 To 25 'Take 25 pressure readings for each tube and atmosphere BrFull(mV, 1, mV25,4, VX1, 1, 2500, true, true, 0, _60Hz, 1, 0) Sum = Sum + mV Next j Valve(i)= Sum/25 'Average the 25 readings from upper and lower tube and atmosphere PortSet(1,0) 'Close valve to lower tube PortSet(2,0) 'Close Valve to upper tube PortSet(3,0) 'Close Valve to atmosphere Next i Delta_mV = Valve(2) - Valve(1) Mult = Delta_H/Delta_mV Offset = (Valve(3) * Mult) WtrLvl = Valve(2)* Mult – Offset 'units of WtrLvl are same units as Delta_H (a constant) CallTable Table1 NextScan EndProg 5.2 CR10(X) Example Input Location Usage: LOCATION LABEL #1: Liquid Level #4: Multiplier #5: Offset #6: mv/V #7: Sum #8: Avg. Level #9: mV/V#1 #10: mV/V#2 #11: mV/V#3 #12: Delta V #13: Delta h * Table 1 Programs 01: 60 Sec. Execution Interval 1: Do (P86) 1: 2 Call Subroutine 2 2: Do (P86) 1: 42 Set high Port 2 3: Excitation with Delay (P22) 1: 1 EX Chan 2: 0 Delay w/EX (units=.01sec) 3: 150 Delay after EX (units=.01sec) 4: 0 mV Excitation Subroutine 1 measures the pressure in the tubing connected to the second value: 4: Do (P86) 1: 1 Call Subroutine 1 5: Do (P86) 1: 52 Set low Port 2 The following instructions convert the mV readings to engineering units: 6: Z=X*Y (P36) 1: 8 X Loc AVG LEVEL 2: 4 Y Loc MULT. 3: 1 Z Loc [:LEVEL#1 ] 7: Z=X+Y (P33) 1: 1 X Loc LEVEL#1 2: 5 Y Loc O...