## 3 Research and Development of the Experimental Setup
### Device Composition and Structure  
The whole equipment adopts the design of a variable temperature field and multiple pipelines, which can carry out five online densitometers and three kinds of liquid experiments at the same time. It consists of a thermostatic stirring control system, walk-in thermostatic field, high-precision benchtop densitometer, pipeline pressurization system, blowing system, and frequency acquisition system. The main standard uses the high-precision Anton Paar 5000, while the first-class densitometer group is used as the period of verification. Figure 4 shows the Anton Paar 5000 and first class densitometer sets  
The composition of the whole set of experimental equipment and the object is shown in Figure 5.Temperature is one of the most important parameters affecting density change. The liquid in the circulation system is in a stable state to determine a stable vibration frequency. The constant-temperature tank adopts an internal and external double-layer design. The internal circulation system adopts a heatless magnetic stirring pump, which effectively prevents the pump from affecting the temperature field of the tank due to its own heat generation. The outer tank and inner tank are uniformly distributed around the four pieces of guide plate, which effectively ensures the uniformity of the fluid flow in the outer tank, and realizes the turbulence of the flow field in the inner tank and a high degree of uniformity of the temperature field. The volume ratio of the inner and outer tanks is 0.51, which can meet the requirements of low energy consumption and full pipe flow at the same  
Figure 4: Anton Paar 5000 and first-class densitometer set.  
Figure 3: Traceability chain for online vibrating tube density measurements.  
time, and all the pipes in the whole system are insulated to ensure that the temperature change in the process of liquid circulation is in a small change interval.  
The composition of the high-precision thermostat tank and the inner and outer tanks of the thermostat tank is shown in Figure 6. In order to reduce the stress on both ends of the vibration tube's vibration impact, a density meter and the device to make the flange bolt connection are used. Vibration tube frequency measurement by the liquid temperature changes has a greater impact on the import and export of the experimental densitometer installed \(U=0.02\ ^{\circ}C\), \(k=2\) thermometer. The thermometer installed in the flange at one end of the experimental densitometer at an angle of 45\({}^{\circ}\) can not only accurately measure the temperature, but can also effectively avoid the thermometer flange hole in the liquid residue.  
Figure 5: Online vibrating tube liquid densitometer experimental device: general view. 1., 2., and 3. Thermostat tank; 4. System control cabinet; 5. Experimental densitometer; 6. Connecting densitometer flange; 7. Thermometer interface; 8. Walk-in thermostat boxes; 9. Piping connector; 10. Thermostat box control system.  
Figure 6: Inner and outer tanks of the thermostat. 1. LCD control board; 2. Outer tank circulation pump; 3. Inner tank agitator; 4. Inner tank body; 5. Liquid circulation inlet; 6. Temperature sensor; 7. Outer tank body; 8. Deflector plate.  
Densitometer inlet flange connector and outlet separator structure, as shown in Figure 7. The system adopts the bottom-up liquid inlet mode, the circulating liquid is divided into five channels after flowing out of the thermostatic tank through the degassing system, corresponding to five different experimental stations, so it can realize the simultaneous experiments of five densitometers with three kinds of liquids. In order to prevent the experimental error caused by mixing liquids during the experiment, after the experiment on different liquids is finished, the corresponding pipe is purged and the frequency of the empty pipe is compared to check whether it was purged well. The structure of the standard liquid dispenser is shown in Figure 8.