What is a Pressure Switch?

The pressure switch uses high-precision, high-stability pressure sensors and transmission circuits, and then uses special CPU modular signal processing technology to achieve the detection, display, alarm and control signal output of the medium pressure signal. Pressure switches can be widely used in petroleum, chemical, metallurgy, power, water supply and other fields to measure and control the gauge and absolute pressure of various gases and liquids. It is an ideal intelligent measurement and control instrument for industrial sites. Pressure switches are widely used in the aerospace and military industries, such as M1A1 tanks, Apollo spacecraft, Boeing 747, Airbus A320, F22, F117 and other products.

There are two types of pressure switches: mechanical and electronic.

1. Set the method of controlling pressure

(1) Short press the (ON / OFF) running key to turn off the running indicator and the pressure control system to turn off.

(2) Set the upper / lower control limit

Short press the SET key once to enter the lower limit setting state (the corresponding lower limit indicator is on). Set the value with () (). After setting the lower limit, press the SET key shortly to enter the upper limit setting.

(3) After the setting is completed, press the SET key to automatically save the set value to the computer chip (after the parameter is modified, no key operation within 5 seconds will automatically save the current parameter setting).

(4) Press the (ON / OFF) running key again (the corresponding running indicator lights up), and the motor starts to work.

2. Unit switching method: short press the (ON / OFF) running key to turn off the running indicator light, short press the increase key () to switch the unit arbitrarily between MPa, Kg / cm, and PSI. After the setting is completed, turn on the running indicator.

3. Zero reset function: short press (ON / OFF) running key to turn off the running indicator, long press decrease key () for 5 seconds to clear the current pressure value and correct the zero error. After the setting is completed, turn on the running indicator. (The pressure switch must not apply pressure when using this function.)

System function mode

Press and hold the SET button for 3 seconds to enter the system settings, and then press the SET button briefly to display the following function modes in sequence.

After setting all function modes, press the (ON / OFF) run key to automatically store the set value into the computer chip.

Function mode	Detailed function	effect	Setting method
POST R001 / R000 Close / open	Function open: The relay stays closed for 1 minute after starting, even if the pressure exceeds the upper limit set value, the relay will not open.	Prevents the motor from starting frequently when the pressure in the pipe changes momentarily when the motor is just started.	After entering the system settings, you can use the increase () / decrease () keys to turn the function on or off, and underlined means the default function.
Automatic pressure detection S000 / S001 switch on switch off	Function on: After the relay is closed, the controller will not detect the pressure change for 3 minutes, it will automatically disconnect the relay, and the screen will display "E--1".	Avoid motor idling caused by the drain of water source, leaking pressure of pipeline, etc., which caused the measured pressure not to reach the set upper limit value for a long time.	After entering the system settings, use the increase () / decrease () keys to turn the function on or off.
Overpressure self-test N001 / N000 Close / open	Function open: When the pressure is greater than (upper limit + 0.1MPa), the relay is disconnected, and the screen alarm displays "E--2". When the pressure is lower than (upper limit + 0.1MPa), the alarm is cancelled and the controller resumes work.	Remind the customer that the control system has a pressure exceeding the upper limit of control. Please check the system for abnormalities.	After entering the system settings, use the increase () / decrease () keys to turn the function on or off.
Control delay H001 / H000 Off / On	Function ON: When the pressure reaches the operating point, the controller does not act immediately, and the action is delayed. The time of the action can be set.	Setting the control delay can prevent the motor from starting frequently and damaging the motor due to the unstable pressure in the tube.	After switching from H001 to H000, press the SET key momentarily to display "0010". Use the () () keys to change this value. The unit is second. The default is 10 seconds. Press the SET key to save the setting and exit.
Parameter protection P001 / P000 Close / open	Function ON: Press any key except (ON / OFF) running key, the screen will display "----", at this time, you need to enter the password to set parameters such as upper and lower limits.	Protect the parameters set by the engineering staff from being modified.	When "----" is displayed, press the () key to enter the password, the SET key is shifted, and the password is "1111". After pressing the SET key to confirm, you can set the parameters. When the system restarts, it will automatically enter the password protection function.

Function definition: " * 00 1" ( mode is off ) , " * 00 0" ( mode is on ) , underlined indicates the factory default mode

The working principle of the pressure switch: When the pressure in the system is higher or lower than the rated safe pressure, the disc in the sensor moves momentarily, and the switch connector is pushed on or off by the connecting guide rod. When the pressure drops or rises, At the rated recovery value, the disc is instantly reset, and the switch is automatically reset, or simply when the measured pressure exceeds the rated value, the free end of the elastic element is displaced, and the switching element is pushed directly or after comparison to change the switching element. On-off state, to achieve the purpose of controlling the measured pressure. The elastic elements used in the pressure switch include single coil spring tube, diaphragm, diaphragm box and bellows. ^[2]

Pressure switches are widely used in high, low pressure protection control of household, commercial and automotive refrigeration systems, steam conditions and power stations;

Accuracy: A value representing the accuracy of the equipment, including linearity, tolerance, hysteresis, repeatability, etc. At present, the highest accuracy of Nagano's pressure switch can reach ± 0.5% FS, and the model is CB33.

Maximum pressure (Max.P): The maximum value of the pressure range.

Full scale (FS): The difference between the maximum and minimum pressure ranges.

Connection difference (dead zone): refers to the difference between the set action value and the reset value of the switch. For example, when the setting value is 1 MPa and the actual reset value is 0.9 MPa, the connection difference is 0.1 MPa.

Working temperature: refers to the temperature range where the instrument's internal mechanism and sensitive components will not continue to deform during operation. Generally, the recommended operating temperature range of the pressure switch is -5 ~ 400C. If the temperature of the medium is too high, you can consider adding an accessory siphon (filling) to reduce the temperature.

SPDT (Single Pole Double Throw): It consists of a normally open, a normally closed contact and a common terminal.

DPDT (Double Pole Double Throw): It consists of a symmetrical left and right common end, two sets of normally open and normally closed terminals.

Upper limit one contact (normally open): When the pressure rises to the set value, the contact will act and the circuit will conduct.

Lower limit one contact (normally closed): When the pressure drops to the set value, the contact will act and the circuit will conduct.

Upper and lower limit two contact HL: It is a combination of upper limit and lower limit. It is divided into two types: independent operation of two contacts (double setting, double circuit) and simultaneous operation of two contacts (single setting, double circuit).

Upper limit 2 contact: Combined two upper limit forms, divided into two types: independent operation of two contacts (dual setting, dual circuit) and simultaneous operation of two contacts (single setting, dual circuit).

Lower limit 2 contact: Combines two lower limit forms, which are divided into two types: independent operation of two contacts (dual setting, dual circuit) and simultaneous operation of two contacts (single setting, dual circuit).

Pressure resistance: The maximum pressure that the pressure switch can withstand its normal performance. However, when the pressure switch is used in an overpressure situation, the sensitive components will continue to deform, and the pressure set value will change, and the pressure switch will not be able to exert its normal performance and may even be damaged.

IP (Protection Level): A standard drafted by the International Electrotechnical Association (IEC) regarding the dust and moisture resistance of lamps. ^[3]