1 overview of electronic truck scale
The truck scale is a compulsory verification measuring instrument stipulated by the state. After each overhaul or commissioning, it can be used only after passing the verification of the legal metrological verification organization.
1.1 system composition
SCS series electronic truck scale is usually composed of scale platform, load cell, connector, limit device, junction box, weighing display instrument and other parts. According to the use requirements, external equipment such as printer, large screen display, computer, weighing software, regulated power supply and UPS can be selected.
1.2 working principle
The weighed weight or truck is placed on the scale platform. Under the action of gravity, the scale platform transmits the gravity to the load-bearing support head, causing the elastomer of the load cell to deform. The bridge of the strain gauge attached to the elastomer strain beam loses balance, outputs an electrical signal proportional to the weight value, amplifies the signal through the linear amplifier, and then converts it into a digital signal through the A / D circuit, After the signal is processed by the microprocessor (CPU) of the instrument, the weight data is directly displayed, and the weighing data is printed and recorded by the printer. If the computer is configured, the measurement data can be input into the computer management system for comprehensive management.

2 technical indicators
2.1 main technical indexes of truck scale
2.1.1 maximum weighing: 10t-150t
2.1.2 table size: 2.5m × 6m~3m × 24m and other table sizes are optional
2.1.3 accuracy level: OIML III
2.1.4 maximum division number: n = 3000 ~ 6000.
2.1.5 calibration division value: 0-20t: ± 20kg, 20-80t: ± 40kg, > 80t: ± 60kg
2.1.6 display division value: 0-60t: ± 20kg, ＞ 80t: ± 50kg
2.1.7 working environment: temperature - 10 ~ 45 ℃, relative humidity no more than 95% RH.
2.1.8 power supply: 220VAC (- 7% ~ + 7%) 50Hz.
2.1.9 it has the functions of zero setting, automatic zero tracking, power-off data protection, fault self diagnosis, etc.
2.2 main technical indexes of sensor
2.2.1 single maximum range: 40t
2.2.1 sensitivity: 2mV / V
2.2.2 comprehensive error: ± 0.03%
2.2.3 safety overload: 150%
2.2.4 input impedance: 375 ± 1 Ω
2.2.5 output impedance: 370 ± 1 Ω
2.2.6 insulation resistance: ≥ 5m Ω
2.2.7 safe side load: 100%
2.2.8 limit overload: 400%
2.2.8 number of sensors: select several sensors according to the number of configuration sections of the weighbridge

3 inspection and commissioning
3.1 inspection items
3.1.1 the sensor and extension cable are intact, and the connector is free of oxidation and corrosion.
3.1.2 the central junction box shall be intact without deformation and poor sealing.
3.1.3 the shielding layer of signal cable shall be well grounded, and the insulation resistance to ground between signal lines shall be greater than 5m Ω.
3.1.4 the appearance of the weighing display is intact, and the wiring is correct without looseness.
3.1.5 the weighing table of truck scale shall be free of deformation.
3.2 preparations before commissioning
3.2.1 transfer trial weights, lifting equipment and forklift to the site.
3.2.2 be familiar with the operation instructions of weighing display instrument.
3.2.3 power on the system and preheat the instrument for 15 minutes.
3.2.4 commissioning sequence
When the truck scale leaves the factory, all parameters have been set and standard correction has been carried out. When arriving at the site, the offset load adjustment and zero reference adjustment are carried out first, and then the range fine adjustment is carried out. Generally, it is not necessary to reset and correct. Once the sensor, center plate, weighing display instrument and other components are replaced, they need to be reset and corrected.
3.2.4.1 eccentric load adjustment (angle difference adjustment)
After the instrument enters the weighing state, the partial load can be adjusted. Use a certain weight (generally one-fifth of the maximum weight) to press the angle in sequence so that the error of the displayed value of each angle does not exceed the allowable error. If the error exceeds the allowable error, it can be adjusted by modifying the angle coefficient until the octagonal display is consistent. The octagonal coefficient can also be adjusted by automatically adjusting the angular coefficient.
3.2.4.2 zero reference adjustment
After the truck scale is installed or overhauled on site for the first time, the zero reference must be determined again. When the scale platform is empty, press the "set to zero" key, or enter the menu to perform zero calibration.
3.2.4.3 range adjustment
Range adjustment is actually to adjust the linear slope. If the actual input display value is shown as the dotted line, the output linearity can be made to meet the ideal state through the range adjustment function of the instrument
The steps of range trimming are as follows:
a. Before using the range adjustment function, the standard correction must be set first. Although the minimum value of the test weight does not have to be greater than 10% of the full range, the weight used in practice should be as many as possible.
b. Enter to perform zero calibration.
c. Load the known silicon code on the scale platform and perform range calibration.

4 maintenance and fault inspection
4.1 allowable axle load
4.1.1 the maximum load of the weighed vehicle shall not exceed the maximum weight of the scale.
4.1.2 the axle load of the truck scale is 40t.
4.1.3 the allowable axle load of the truck scale is related to the sensor capacity, sensor fulcrum distance and other factors. Generally, the truck scale is prohibited to be close to the forklift with the maximum weight and the vehicles with short wheelbase.
4.1.4 when the vehicle drives into the weighing platform, the speed should be less than 5km / h, drive into the weighing platform in a straight line, then brake slowly, measure after the vehicle stops stably, and stay in the center of the weighing platform as far as possible.
4.2 scale platform maintenance
4.2.1 the clearance around the weighing platform shall be uniform and reasonable (the clearance is 10 ~ 15mm), and there shall be no stones, iron blocks and other foreign matters stuck.
4.2.2 regularly check whether the limit clearance is maintained at 2 ~ 3mm, and the limit bolt shall not collide with the scale body.
4.2.3 the connector shall be maintained every six months, and the bearing head shall be coated with butter.
4.2.4 the platform of the scale shall be cleaned frequently and kept clean. The surface paint shall be repainted regularly (it is recommended to do it once a year).
4.2.5 it is forbidden to carry out arc welding on the scale platform. If it is necessary to carry out arc welding on the scale platform, please pay attention to the following points:
a. Disconnect the signal cable from the instrument.
b. The ground wire of arc welding must be set near the welded part and firmly contact the scale body.
c. Never make the sensor part of the arc circuit.
4.3 instrument maintenance
4.3.1 the warm-up of the instrument is generally about 15 minutes. It is strictly prohibited to turn on the instrument power when the scale platform is loaded.
4.3.2 regularly check whether the line wiring is loose, broken and whether the grounding wire is firm.
4.3.3 the junction box shall be kept dry and clean, and the desiccant in the box shall be changed regularly. Once the wet air and water in the junction box drip into people, it can be dried with an electric hair dryer.
4.4 sensor replacement
Once any sensor is found to be damaged, replace it according to the following steps:
a. If the upper part of the scale support (lifting platform) is damaged, use the jack to open the upper part of the scale support (lifting platform) and take out the cover plate of the scale.
b. Open the junction box, disconnect the damaged sensor cable from the junction box, remove the cable clamp fixing the cable, and pull out the cable at the sensor end.
c. Loosen the high-strength nut fixing the sensor with a socket wrench, remove the sensor, install a new sensor, fix the sensor with high-strength bolts and nuts, and then tighten the nut with a torque wrench according to the specified torque, and the specified tightening torque of the sensor for truck scale.
Sensor capacity: 30T
Specification of fastening bolt: M24
Tightening torque: n • m 450   Kg•m 45
d. Pass the new sensor cable through the scale body into the junction box, and fix the cable with a cable clamp.
e. Fix (or solder) each core of the cable on the corresponding terminal post or solder joint of the junction box.
f. Install the connector (grease the bearing head) and the limit support, loosen the jack, level the scale platform, and cover the cover plate.
g. After replacing the sensor, the truck scale must be recalibrated.
4.5 instrument PCB replacement
For the truck scale used frequently, once the instrument is damaged, it is difficult to find the fault for the moment. In order not to affect the use of the truck scale, the instrument PCB main board can be replaced quickly. The steps to replace the PCB motherboard are as follows:
a. Cut off the power supply of the instrument.
b. Open the instrument, disconnect all connectors on the PCB and record the position of the connectors.
c. Remove the screws fixing the PCB board and remove the PCB board.
d. Install the new PCB board (place the shielding layer in the fixed position at the same time) and fasten it with screws.
e. Insert the connector in the correct position.
f. After a new PCB board is replaced, the parameters and calibration must be reset.
4.6 fault inspection
4.6.1 find fault location
If the truck scale fails to work, the first step is to find out where the fault occurs. The simplest way is to find it with the help of the simulator. The steps are as follows:
a. Disconnect the signal cable from the junction box to the instrument, and insert the socket of the simulator (nine core D-shaped flat socket) into the instrument interface.
b. Turn on the power and check whether the instrument works normally. If the instrument works normally, it indicates that the fault is on the scale platform. If the instrument does not work normally, the fault is on the instrument.
4.6.2 fault analysis of weighing platform
a. First check the junction box for water vapor intrusion. If there is water vapor, scrub it with alcohol, and then clean the interior with electric wind.
b. Find out whether there is a short circuit in the wiring. In the junction box, use a multimeter to measure the resistance between the shielded wire (SH, yellow) and other wires and the scale platform, and check whether there is a short circuit. At the same time, check whether there is a short circuit between each wire and the ground wire or the stainless steel shielded wire outside the signal wire cable. If there is a short circuit, replace the cable, and check the sensor if there is no fault.
4.6.3 steps for finding sensor faults
a. In the junction box, disassemble the sensor wiring, use a multimeter to measure the resistance between positive excitation (+ Ex) and negative excitation (- ex) of each sensor, and the resistance value is about 770 Ω. Use a multimeter to measure the resistance between positive output (+ SEN) and negative output (- sen) of each sensor, and the resistance value is about 700 Ω. If the resistance value is found to be incorrect, continue to find it in the next step.
b. Put the weights on each section of the weighing platform in turn. If the indication value of which section is found to be incorrect, put the weights on each corner of the sensor of this section (pressure angle), find out the bad sensor, and replace the sensor according to Article 4.4 of this section. Or disconnect the + Sen and - sen terminals of a sensor, and measure the resistance value when it is not powered on, which should be about 700 Ω. When it is powered on, measure the DC voltage at both ends, set the sensor capacity as K, and the actual pressure it receives is F. if 8142 instrument is used, the voltage value is: u = U0 * s * f / K (MV), where U0 is the excitation voltage and S is the sensitivity of the sensor.
4.7 common faults and treatment
No display of the instrument after startup: check whether the power plug is firmly inserted or disconnected, check the regulated power supply, check the power supply part of the instrument, and check the fuse;

Power failure: the instrument is damaged. Replace the instrument
Display digital instability and drift, poor wire contact, and check each wire connector;
If the output of the regulated power supply is poor, check the output of the regulated power supply with a multimeter;

Damp in the junction box: dry it with an electric hair dryer;

Sensor failure: see 4.6.3 in this section

Instrument failure: replace the instrument
The display of weighing data suddenly exceeds a lot of errors: the scale platform is inflexible, there are foreign matters stuck in the limit, check the clearance around the scale platform and eliminate foreign matters; Device failure and adjustment of limit clearance;

Sensor failure: see 4.6.2 in this section
4.8 maintenance
The verification cycle of electronic truck scale is 1 year. Before verification, the truck scale must be overhauled and debugged according to the contents of this regulation.