The thermal flow switch adopts precision electronic components widely used in aviation and automobiles, and its reliable and stable circuit design makes the flow signal more accurate and stable. Currently, it has been widely used in industries such as steel, metallurgy, pharmaceuticals, and chemical engineering
The ZH-L2 thermal flow switch is an upgraded version of the ZH-L1 model, which not only has more prominent improvements in the signal processing of the flow switch probe, but also makes the HL-L2 software operation and control functions more powerful; Easy to operate and easy to install.

The measuring principle of the ZH-L2 thermal flow switch is the same as that of the ZH-L1, and it is also designed based on the principle of heat exchange. The probe is equipped with a heating module and a heat sensing module, and the heat dissipation of the heating module is closely related to the flow rate of the measured fluid. If there is no medium flow in the pipeline, the signal received by the heat sensing circuit is a fixed value; When the fluid medium flows through the probe, the signal received by the thermal circuit changes with the flow rate of the medium. The thermal circuit converts the temperature difference signal between the heating module and the thermal module into an electrical signal, and the processor then converts it into signals such as PNP/NPN/4-20mA/relay for output.
Gas liquid dual purpose, can be used for gas and hydraulic systems, circulating water, cutting fluid and lubricating oil cutoff monitoring, and pump idle protection.

Table 2 Comparison Table of the Relationship between Liquid Level Flange and Minimum Range

The minimum range of the differential pressure liquid level transmitter should be the larger value of the minimum range in Table 1 and Table 2. The adjusted range shall not be less than the minimum range. The maximum range of the liquid level transmitter should be the minimum of the maximum range of the transmitter body and the rated pressure of the liquid level flange.
4 output signals
2-wire system, 4-20mADC HART output, digital communication, with HART protocol loaded on 4-20mADC signal.
Output signal limit: Imin=3.9mA, Imax=20.mA
Alarm current (mode can be set)
Low alarm mode (minimum): 3.7 mA
High alarm mode (maximum): 21 mA
No alarm mode (hold): maintain the effective current value before the fault
Alarm current standard setting: high alarm mode
5 Response time
The damping constant of the amplifier component is 0.1s; The time constant of the sensor and liquid level flange is 0.2-2 seconds, depending on the range and range ratio. The additional adjustable time constant is 0.1~60s.
6 General conditions
6.1 Installation conditions
The liquid level flange transmitter can be directly fixed in any position. The optimal state is to keep the process flange axis in a vertical position, and the positional deviation will result in a correctable zero offset. The electronic watch case can rotate up to 360 °, and the positioning screw can fix it in any position.
6.2 Environmental conditions
ambient temperature
Minimum: depending on the filling fluid
Maximum: 85 ℃
When equipped with LCD display and fluororubber sealing ring, -20~65 ℃
Storage temperature/transportation temperature
Minimum: depending on the filling fluid
Maximum: 85 ℃
Relative humidity
0-100%
Impact resistance
Acceleration: 50g
Duration: 11ms
Anti vibration
2g to 500Hz
Electromagnetic compatibility (EMC)
See Table 3 "Electromagnetic Compatibility Schedule" on the next page
6.3 Process Medium Limits
Medium temperature limit: -30~180 ℃
Transmitter body pressure limit
From an absolute pressure of 3.5kPa to the rated pressure, the protective pressure can be greater than 1.5 times the rated pressure and applied to both sides of the transmitter.
Rated pressure of liquid level flange
ANSI standard: 150psi~600psi
DIN standard: PN 1.6MPa~PN 10MPa
Unidirectional overload limit
The low pressure side is the rated pressure of the transmitter body, and the high pressure side is the rated pressure of the liquid level flange, which may cause adjustable zero drift.
Weight: DN 50/2 "approximately 7-10kg; DN 80/3 "approximately 8-11kg; DN 4 "is approximately 9-12kg.
Explosion proof performance
NEPSI Flameproof License: Ex d Ⅱ C T6
NEPSI Intrinsic Safety License: Ex ia IIC T4
Permissible operating temperature: -40 ℃~65 ℃
6.4 Power supply and load conditions
The power supply voltage is 24V
R ≤ (Us-12V)/Imax k Ω
Where Imax=23 mA
Maximum power supply voltage: 42VDC
Minimum power supply voltage

Note: (1) A performance level description: During testing, the performance is normal within the technical specification limits.
(2) B performance level description: During testing, the function or performance is temporarily reduced or lost, but it can recover on its own, and the actual operating status, storage, and data remain unchanged.
External dimension unit (mm)

Table 4 Structural dimensions of liquid level flange

Note: Users can choose to install bolts and nuts.
7 Electrical connection diagram

Note: The quick interface function is equivalent to the signal terminal.
8. Instructions for Low Voltage End Process Connection