Hello everyone, welcome to the Star Instrument Classroom, in this issue, we will talk about the difference between passive signals and active signals. 1. Definition of passive signal and active signal For current signals, if the device has an independent working power line, the signal output (such as 4-20mA) provided by the device is an active signal; If the device itself does not have an independent working power supply, the signal it provides is a passive signal. The output signal of the three-wire instrument and the four-wire instrument is an active signal, and the output of the two-wire instrument is a passive signal. 2. How to collect passive signals and active signals For the acquisition of active signals, it is very simple, first of all, it is necessary to connect the power supply of the signal source equipment (usually there are two kinds of three-wire system and four-wire system) to make the device work normally, and secondly, the positive and negative ends of the input interface of the acquisition device are connected to the positive and negative ends of the signal source equipment respectively. For the acquisition of passive signals, a DC 24V power supply is first needed (because the two-wire instrument that provides passive signals does not have an independent working power supply, when it needs to output 4-20mA signals, its working voltage needs to be provided by external equipment. This DC24V power supply can be an independent power supply, or it can be provided by the power distribution function of the passive signal acquisition equipment); Secondly, the correct circuit should be formed between the two-wire instrument, the DC24V power supply and the passive signal acquisition equipment: the positive pole of the DC24V power supply is connected to the positive pole of the 4-20mA output of the two-wire instrument, the negative pole of the 4-20mA output of the two-wire instrument is connected to the positive pole of the 4-20mA signal input end of the acquisition device, and the negative pole of the 4-20mA signal input end of the acquisition equipment is connected to the negative pole of the DC24V power supply, so that a complete loop is formed. Star Meter Manufacturing Co., Ltd. is a high-tech enterprise integrating R&D, production and sales. Specializing in the production of pressure transmitters, liquid level transmitters, temperature transmitters, temperature and humidity transmitters, differential pressure transmitters, soil moisture transmitters, 3051 transmitters and related instrumentation accessories. A number of products under the Xingyi brand have obtained a number of patent certificates issued by the state, such as CE certification, IS9001 certification, SGS certification, TüV SüD certification, explosion-proof certification, etc. If you have any questions about product consultation, product customization, agency, technical inquiry, quotation, etc., please contact Xingyi: 400-600-4496!