LJ12-1A Portable current meterDetailed product description：

The LJ12-1A/C rotary propeller flowmeter has a small size, light weight, and is easy to carry. It is suitable for small rivers, channels, runoff experimental stations, water conservancy investigations, and environmental sewage monitoring. It is used to measure the average flow velocity at predetermined measurement points in the water crossing section during the specified time period. Equipped with the CBL-1 pump station flowmeter measuring rod, it can measure the flow rate of small and medium-sized pump stations. Paired with the integrated suspension sampler for measuring flow velocity. Installing suspension shaft components can measure flow in deep water.

2 LJ12-1A portable propeller flowmeter model
According to the installation method of flow measurement and the structure of the signal reduction transmission part:
LJ12-1A type - installation measuring rod diameter of Φ 16mm, each signal rotation speed: 20 revolutions;
LJ12-1C type - installation measuring rod diameter of Φ 16mm, each signal rotation speed: 1 rotation;
The structure of the two types of instruments is basically the same, only type A is introduced.

Main technical indicators of the propeller type flowmeter
⑴ Spiral propeller structure: spiral curved three bladed, left-handed, PC engineering plastic
⑵ Rotary diameter of propeller D: 60mm
⑶ Hydraulic pitch of propeller b: 120mm
⑷ Instrument starting speed V0: ≤ 0.06m/s
⑸ Flow velocity measurement range V: 0.07-7m/s
⑹ Signal component structure: Magnetic sensitive reed switch electronic switch
When the relative error of the calibration curve E: V ≥ 0.2m/s, E ≤± 1.5%;
When V<0.2m/s, E ≤± 5%
⑻ Switch contact capacity: current ≤ 50mA, voltage ≤ 6V
Working frequency of reed switch: 70 million times
Continuous working time of the instrument: 2 hours (when the sediment concentration is ≤ 0.5kg/m3 and the water depth is ≤ 1m/s)
⑾ Instrument installation measuring rod specification: CG16-1 type
12. Rotation angle of suspension shaft components: LJ12-2A/C type - horizontal 360 °, vertical 20 °
13. Working water flow conditions of the instrument
Water depth range: When equipped with a measuring rod, the lower limit is 0.1m, and the upper limit depends on the length of the measuring rod;
When measuring flow with suspension shaft components, 0.5-40m
Water temperature: 0-40 ℃
Suspended sediment concentration: ≤ 10kg/m3
Working principle, flow velocity measurement and calculation method of 4 flow meters
4.1 Working principle of flowmeter
The working principle of the flowmeter is based on the fact that when water flows on the propeller, it produces a rotational motion, and there is a certain functional relationship between its speed and the flow velocity V: V=f (n). Using a flowmeter to calibrate the water tank experiment, establish a calibration formula that approximates a straight line above the critical flow velocity VK and is expressed using an empirical formula
V=a+bn (1)
In the formula, V is the flow velocity: a is an additional constant. After determining the structural parameters of the propeller, it mainly depends on the internal friction torque M of the main engine; b is the hydraulic torque of the propeller. When the value of M is small and stable, it mainly depends on the structural parameters of the propeller, such as the mechanical lead, shape resistance, surface resistance, etc; N is the rotational speed of the propeller, N is the rotational speed of the propeller during the speed measurement period T, that is, n=N/T. The rotational speed N is the product of the number of signals R output by the instrument and each signal representing the rotational speed Z of the propeller, that is, N-ZR.
In the low-speed zone below VK, the hydrodynamic moment ML of the water flow is very small, and it can only barely overcome the internal friction of the instrument to push the propeller to rotate. Therefore, the low-speed V-f (n) relationship exhibits a curved form due to the occurrence of slip operation caused by obstruction during the operation of the propeller. Provide a V-n relationship curve or an approximate linear formula for the verification results.
4.2 Flow velocity measurement method
The measurement of flow velocity and flow rate using a propeller flowmeter should follow the methods specified in hydrological measurement standards. For the selection of test sections, channel locations, layout of survey lines, number of vertical survey points, and flow calculation methods, please refer to Volume 4 and Volume 2 of the "Hydrological Testing Standards" compiled by the Hydrological Department of the Ministry of Water Resources. The installation of the flowmeter should be based on the water flow conditions, as shown in Figures 1-4. Place the instrument at the designated measurement point and secure it. The measurement duration is generally 100 seconds for flow rate and 200 seconds for low speed. Based on the number of signals R output by the flow meter within the measurement duration T, the actual rotation speed N of the instrument can be calculated, and then the flow rate can be calculated.
4.3 Flow velocity calculation method
Example: LJ12-2A rotary propeller flowmeter, calibration formula: V=0.120n+0.010, signal component structure is 20 revolutions per signal, actual rotation speed N=ZR, that is, N=20 × R. After measuring the speed for T=100 seconds, the number of signals measured is R=50. Based on this, the flow velocity can be calculated. Firstly, calculate the actual number of revolutions N=20 × 50=1000 revolutions, and substitute it into formula (1):
V=0.120×1000/100+0.010=1.21m/s
5 Instrument Structure
The appearance of the LJ12-2A/C rotary propeller flowmeter is shown in Figure 5, which can be divided into two parts: the instrument host and the tail wing. Figure 6 shows the main structure of the LJ12-2A/C propeller flowmeter, which can be divided into four parts according to its working principle: propeller, rotating support system, signal conversion generation part, and instrument base. A. The structural difference of the C-type instrument is only the signal reduction transmission part in the rotating support system 2A/C, and the rest is completely the same.
5.1 Propeller
The propeller structure includes three spiral curved blades (left-handed), a propeller column, and a guide cap. The inner cavity of the propeller column is a precise cylindrical hole with M9 × 1 threads for coordination with the rotating support system; The guide cap is a streamlined blade head, and the rotating outer profile of the propeller has a good streamline shape and low water resistance. The forward projection area of the propeller blades is relatively large, which increases the hydrodynamic torque and therefore has good low-speed performance. The propeller material is made of high-quality engineering plastic made of PC, which has good impact resistance, resistance to atmospheric aging, and thermal stability.
5.2 LJ12-2A type propeller flowmeter support system
The rotating support system (component) is the core of this series of propeller flow meters, and the structure of the LJ12-2A instrument is shown in Figure 7.
The rotating support system includes: rotating part, rotating shaft dynamic sealing part, rotating support part, and signal conversion generation part.
5.2.1 Rotating parts (ball bearing support components)
Composed of propeller shaft, propeller shaft sealing ring, front and rear ball bearings, inner spacer and bearing inner ring cap screw sleeve, etc. The front and rear ball bearings are positioned with inner spacers in the middle and installed on the rotating shaft. The rear end is tightened and fixed with a bearing inner ring and cap screw sleeve, forming the rotating part base. As shown in Figure 7. Overall, the rotating part should also include the propeller sleeve and the dynamic sleeve in the toothed sealing device, as shown in Figure 6. The front and rear ball bearings are stainless steel precision instrument single row radial ball bearings: 8 series 20000086MX, 9 series 1000096MX, with a starting friction torque of 0.5-1.0g.cm; The rotating shaft is made of 9Cr18 stainless steel with a diameter of 6 × 85mm, which has good structural rigidity and high manufacturing accuracy. The concentricity is less than 0.01mm, providing a high-precision, stable and reliable rotating support foundation for the support system of this series of instruments. It has low and stable frictional torque and rust prevention ability.
5.2.2 Dynamic sealing part of rotating shaft
Adopting a non-contact labyrinth seal structure, consisting of several pairs of dynamic and static sleeves that are interlocked to form a winding and small gap path (Figure 7), it can reduce pressure and dissipate energy for the entry of river water, thereby slowing down the entry of river water into the bearing oil chamber. Divided into front and rear stages: The front stage a is a rotating sleeve type, consisting of a propeller rotating sleeve, a rolling flower and tightening nut, and a static sleeve at the rear edge of a grate type sealing device; The rear stage b is of the grate tooth type (enlarged in Figure 9), and the dynamic and static sleeves are assembled into a whole with a grate tooth type, which has better sealing effect and is installed in front of the bearing oil chamber c.
To ensure the sensitivity of the instrument, the axial and radial clearance should be tested before assembly: 0.2-0.3mm.
5.2.3 Supporting parts
Composed of bearing seat, bearing seat sealing ring, and instrument seat sealing ring, it is used for installing rotating parts, dynamic sealing of rotating shafts, and signal conversion parts. The middle column chamber of the bearing seat serves as the bearing oil chamber (Figure 10).
5.2.4 Signal Conversion and Generation Section
The signal conversion and generation part includes three functions: mechanical motion conversion, deceleration, and signal generation. The deceleration ratio of Type A instrument is 1:20; Type C is 1:1.
5.2.4.1 Reduction gear components
Composed of gears, gear seats, gear shafts, gear covers, magnets, and gear shaft clamps (Figure 11), the gear has 20 teeth and is mounted in the gear seat slot, supported by the gear shaft. The magnetic steel is embedded in the belly of the gear, and the N-S pole of the magnetic steel is sealed with a gear cover to rotate around the gear axis.
Gears, gear shafts, and other components are precision instrument parts that are manufactured with high geometric and rotational accuracy (homogeneity, end face perpendicularity, and radial runout), surface smoothness, as well as small and stable frictional torque (average 0.10g. cm), balanced operation, and magnetic steel made of rare earth samarium cobalt (SmCo-2), which has high magnetic energy product and stability.
5.2.4.2 Reed switch support components
As the signal generating part of the magnetic reed switch electronic switch. Composed of reed switch, connecting sleeve, pipe seat, etc., sealed with epoxy resin.
The reed switch is a super miniature normally open structure, with a maximum rated power of 3W for the contacts, a maximum switching current of 0.11A, a maximum initial contact resistance of 200m Ω, a minimum insulation resistance of 107 Ω, and an electrical life (resistive load) of 7 × 106 (6VDC, 20mA).
The reed switch component is installed in the instrument seat outside the bearing oil chamber. It has a wide range of matching parameters with magnetic steel, strong universality, no need for adjustment, and is very easy to replace.
The reed switch is matched with inductive loads (such as electric bell counters). When the contact of the load circuit is open circuited, a high induced voltage will be applied, which will damage the reed switch or reduce its working life. Therefore, it is not suitable to use such load counters.
The instrument signal output uses one wire and another wire with the instrument base as the ground wire, which is output through a measuring rod or steel wire rope. Therefore, it is required that the input impedance of the counter circuit should be relatively large. Otherwise, adhesive tape should be wrapped around the terminal to insulate the wire, terminal, and instrument base, which is inconvenient to use. Therefore, it is recommended to identify professional manufacturers when purchasing counter accessories.
5.2.5 Final assembly of rotating support system
(1) Installation steps
Install the tooth sealing device in the screw hole in front of the bearing seat of the supporting part;
The propeller shaft (including the propeller shaft sealing ring) is installed into the rear hole of the bearing seat and extends from the end;
Install the propeller sleeve at the front end of the propeller shaft and secure it with cylindrical head screws and spring washers;
Fill the bearing seat hole with No. 8 instrument oil (GB487);
Install the front ball bearing, inner spacer sleeve, and rear ball bearing, and tighten them with a screw sleeve on the inner ring of the bearing;
Install the reduction gear component and fill the labyrinth gap of the sealing device with instrument oil. At this point, a small amount of instrument oil should flow out from the inlet gap. The rotating components and rotating support system are fully assembled, and the bearing oil chamber and labyrinth device are also filled with oil (Figure 6).
(2) Detecting axial working clearance
When the ball bearing branch is installed in the bearing hole, there is a certain gap between the front ball bearing and the bottom hole plane of the bearing seat, which is the axial degree of freedom of the inner ring (with steel ball) of the rear ball bearing, ensuring that the natural axial working clearance of the rear bearing, which is also the rotating support system, is 0.05-0.08mm; the friction torque that the bearing should have is 0.5-1.0g.cm, that is, the instrument sensitivity. This structure is debugging free and can randomly replace parts such as ball bearings without affecting the working clearance value. Assembly and maintenance are very convenient. The structure configuration of the rotating and supporting system is reasonable, with a radial runout of the rotating shaft of less than 0.02mm, and good stability during high-speed operation.
(3) Sensitivity of testing instruments
The sensitivity of the propeller flowmeter refers to the internal friction torque of the instrument. The JBM12-2 propeller flowmeter sensitivity tester (torque meter) can be used to scientifically, accurately, and quickly measure the friction torque value, as well as the changes in friction torque during one cycle of operation (20 revolutions for LJ12-1A and LJ12-2A models), the distribution of friction points, and accurately indicate the cleaning of the ball bearing and its assembly quality. Therefore, the sensitivity of the instrument, that is, the starting speed V0, can be accurately calculated to ensure the low-speed measurement accuracy of the instrument. This instrument can be ordered separately. The commonly used methods for measuring stations at present are:; Blowing method, which refers to blowing air evenly and slightly with the mouth aligned with the upstream surface of the propeller, observing the entire process of starting, running, and stopping the propeller. The advantage of this method is that it is simple and easy to implement. It is best to test the new instrument several times to gain experience for future comparison; The disadvantage is that everyone has different work experience and proficiency, and it is not easy to maintain a constant airflow to make the propeller run for one cycle, resulting in poor accuracy.
5.3 Instrument stand
For the installation of the above components and parts, the instrument can be installed in various forms with measuring rods, suspension shafts, etc.
5.4 Instrument assembly
5.4.1 Rotating Support System
There are two red dimples on the bearing seat of the rotating support system, which indicate the N-S direction of the magnetic pole of the reduction gear branch. When the rotating support system is screwed into the instrument seat, attention should be paid to its direction being parallel to the signal component (i.e. reed switch), with a deviation of no more than 20 °.
5.4.2 Propeller
Add instrument oil (about 1/2 height) to the propeller column hole, then hold the outer circle of the rotating sleeve with your right hand and thumb, and hold the propeller with your left hand in a clockwise direction (conventional standard positive spiral) and screw it into the propeller sleeve thread until the propeller sealing ring is tightened.
6 Maintenance
Keep the propeller intact, instrument sensitivity and signal normal to ensure flow measurement accuracy. Therefore, the instrument should be used correctly and maintained, cleaned, and oiled in a timely manner, and the sensitivity of the instrument should be tested at any time.
6.1 General Maintenance
During use, attention should be paid to preventing the instrument from being impacted to avoid damage to precision parts such as propellers and propeller shafts.
When measuring flow, be careful to remove the instrument host from the instrument box, install the tail wing, and check the instrument sensitivity and signal.
⑶ When installing the instrument on the current measuring equipment, attention should be paid to correctness and firmness. Especially when conducting high-speed flow measurements.
After the general flow measurement is completed, the surface of the instrument should be wiped dry with a towel in a timely manner. After checking the sensitivity of the instrument and confirming it is qualified, carefully install the instrument in its original position in the instrument box without disassembling or washing the inside of the instrument.
The instrument has been working in high-speed and high sediment rivers for a long time, and the sealing device may sink sand, affecting the sensitivity of the instrument. In this case, it should be disassembled and cleaned, or sent to the instrument inspection station for maintenance.
The cleaning and refueling interval for ball bearings and oil chambers should be determined through practice based on the water flow conditions, cumulative measurement times and time, and the volatilization of instrument oil at high temperatures during instrument operation.
Each "O" - shaped rubber ring is a key component for sealing the bearing oil chamber. Attention should be paid to its aging, hardening, cracking, and deterioration, and spare parts should be replaced in a timely manner.
Reliability test of signal generating components: Rotate the rotating support system out of the instrument seat hole by 2mm (2 turns), turn the propeller, and the signal should be normal. Otherwise, replace the reed switch spare part or send it to the instrument inspection station for repair.
The room where the instruments are placed should be clean, dry, and well ventilated, with a temperature range of 5-25 ℃ and a small daily temperature difference (to prevent the instrument oil in the instrument oil room from evaporating). The relative humidity should be less than 90%, and there should be no chemicals, acidic, alkaline, or volatile substances near the instruments.
6.2 Cleaning
6.2.1 Cleaning of Instrument Appearance
After measuring in rivers with high sediment content, the sediment and pollutants attached to the surface of the instrument should be washed with clean water in a timely manner, wiped dry with a towel, and the sensitivity of the instrument should be checked and qualified before immediately packing it; If the sensitivity is poor, it should be disassembled, washed, and oiled indoors with good process hygiene conditions. If it still doesn't work, it should be sent to the production plant for inspection.
6.2.2 Disassembly and cleaning of rotary sealing device
After long-term operation in high-speed and high sediment laden rivers, the rotating sealing device may deposit sediment in the labyrinth crevices, affecting the sensitivity of the instrument. Therefore, it should be cleaned in a timely manner. The method is to remove the propeller and propeller sleeve, clean the inner hole of the propeller sleeve and the outer surface of the rotating shaft with gasoline (or clean water) to remove sand, fill the rotating shaft sleeve with instrument oil, install it in the opposite process of disassembly, and then check the sensitivity of the instrument.
6.2.3 Disassembly and cleaning of grate type sealing device
If sediment accumulates in the narrow gaps of the labyrinth of the grate type sealing device, cleaning is more complicated. It can be carefully disassembled and cleaned one by one before reinstalling.
6.2.4 Cleaning of Bearing Oil Chamber
Cover the front hole of the bearing seat with your hand, pour in an appropriate amount of gasoline (No. 120, SY-1207, the same below) from the rear hole, shake it up and down several times, and then pour the dirty oil into the oil storage bottle (filtered as a coarse wash). Repeat the above cleaning process three times and air dry.
6.2.5 Ball bearing cleaning
6.2.5.1 Manual Cleaning (Testing Station)
Ball bearing cleaning is divided into coarse cleaning, semi fine cleaning, and fine cleaning. Cleaning tools: 3 medium-sized aluminum lunch boxes with lids (for cleaning), with a layer of copper wire mesh (65 mesh/25.4mm) set 15mm from the bottom of the box, each box containing about 1/2 of the height of gasoline. Cleaning process: Pinch the inner ring of the ball bearing with your left fingers, and quickly turn the outer ring (with the steel ball) with your right index finger to continuously rotate and roll wash it. Then, perform semi precision washing and precision washing according to the same method. After cleaning, place the ball bearings in the box cover with the mouth facing up on the table (precision washing box) and let them dry. This is the traditional method for cleaning outer ring separated ball bearings, which not only has low cleaning efficiency, oil and time consumption, but also is difficult to clean, especially for non separable ball bearings.
6.2.5.2 Semi automatic cleaning (maintenance station)
As shown in Figure 12, the semi-automatic cleaning machine for ball bearings is used. The spindle of the cleaning head drives the ball bearing to rotate at a high speed of 1400 revolutions per minute, and the mud, debris, and foreign objects in the ball bearing are quickly thrown away. The cleaning efficiency is high, and it is clean, fuel-efficient, and time-saving.
6.2.6 Cleaning of parts related to rotating components
Soak the rotating shaft, inner spacer sleeve, bearing inner ring and cap screw sleeve, reduction gear branch components, etc. in the above three gasoline boxes in sequence, and place them in the box cover with the mouth facing upwards (semi fine washing box, coarse washing box), and let them dry.
6.2.7 Assembly and refueling
Follow section 5.2.5
6.2.8 Oil Quality
This series of instruments is equipped with EccoLube ME18 series oil containing bearing lubricating oil (Eko grease) in the bearing oil chamber. Finally, install the reduction gear component.
6.2.9 Cleaning Process Hygiene
Ball bearings are precision instrument components with high manufacturing accuracy, low and stable friction torque, and high-speed stable operation characteristics. When used with propeller flow meters, they greatly improve instrument performance. However, it must work in a clean oil bath, and any contamination will affect its normal operation, directly affecting instrument performance, measurement accuracy, and even working life. Therefore, during the use of the instrument, the bearing oil chamber should not be filled with river water (sand), and dust and other foreign substances should not be mixed in during cleaning and refueling. For this reason, cleaning utensils, instrument oil, detergents, cleaning workshops, operators, etc. must strictly maintain process hygiene. To prevent hand sweat and other pollution, warm water (about 40 ℃) can be used to wash hands, and hand soap (soap) can be added to degrease and remove dirt to prevent dust pollution. Relevant cleaning and oiling utensils should be placed in the kitchen. The cleaning process requirements for ball bearings are extremely strict, and the conditions of the measuring station are poor. It is recommended that the measuring station be equipped with ball bearing spare parts that have been cleaned thoroughly and meet the torque value standards. Replacement is very convenient and can ensure the performance of the instrument.
6.3 Sensitivity of Testing Instruments
After assembly, the sensitivity of the instrument should be tested according to the requirements of 5.2.5 (3).
7. Usage period
(1) Under normal use, the flowmeter should be recalibrated every year or accumulated 300 hours of operation (whichever is shorter). If the internal friction torque M value of the instrument meets the standard, the propeller is undamaged, and the re inspection time does not exceed two years.
(2) The instrument shall be used normally according to the relevant provisions of this manual, with a service period of 10 years.
(3) If the instrument is damaged or cannot work due to poor manufacturing quality during normal use in accordance with the relevant instructions within one year from the date of receipt, the manufacturer shall be responsible for free repair.
Installation of 8 flow meters for flow measurement
According to the actual situation of hydrological testing, the LJ12 series flowmeter is equipped with multiple installation and measurement methods.
(1) The installation and measurement of hydrological measuring rods have two specifications (diameter × length): CG16-1 type is Φ 16mm × 1.6m, which can be disassembled into two sections; The measuring rod has a decimeter scale and can measure water depth.
According to actual needs, the length of the measuring rod can be extended separately. The measurement method can be carried out on the bridge, shore, or through water. Instrument working water depth: The lower limit is 0.1m; the upper limit depends on the length of the measuring rod, and the required long measuring rod can be ordered separately.
(2) Installation measurement of lead fish head column, LJ1-1A/C instrument can be equipped with lead fish column suspension shaft components installed on the lead fish head column for measurement. The water depth is 1-40m, and the flow velocity is 0.5-7m/s. The measurement method can be carried out on hydrological survey ships or hydrological cable channels. Lead fish weighs 50-700Kg.
(3. Install on the head column of the integrated time suspended sediment sampler, and measure the suspended sediment concentration while measuring the flow velocity to calculate the suspended sediment transport rate.).
(4) Installation of measuring rod for CBL-1 pump station flowmeter, used to measure the flow rate of small and medium-sized pump stations.
Complete set of equipment for 9 instruments
9.1 Instrument itself
1 set of instrument host (equipped with reed switch support components)
9.2 Accessories and Spare Parts
(1) 1 set of dry spring tube branch components
(2) 1 set of spring washer ф 4
(3) 1 cylindrical head screw (M4 × 10mm)
(4) 2 pieces each of various "O" - shaped rubber rings
(ф 16 × 2mm, ф 10 × ф 1.5mm, ф 6 × ф 1.5mm)
(5) 1 oil bottle (containing lubricating oil for oil bearing)
(6) Cross screwdriver (2 inches) 1 piece
(7) One straight shaped clock screwdriver (screwdriver mouth 0.2 × 1.4mm; length 85mm)
(8) Change needle 1 copy
(9) 1 copy of instruction manual
(10) 1 copy of verification certificate
(11) 1 certificate of conformity
(12) 1 instrument box
9.3 Special spare parts (purchased separately by users as needed)
9.3.1 Instrument components
(1) Instrument parts, components, assemblies
(2) Ball bearings (2000086MX, 1000096MX)
(3) Vulnerable parts
9.3.2 Measurement and installation of spare parts
CG16-1 measuring rod, ф 16mm × 1.6mm long (length and number can be ordered separately according to needs)
9.3.3 Testing and Cleaning Equipment
(1) JBM12-2 type propeller flowmeter sensitivity tester (torque meter)
(2) Ball bearing semi-automatic cleaning machine