Three-stage refrigeration atmosphere preconcentrator and temperature control method thereof

The invention relates to a three-stage refrigeration atmosphere pre-concentration instrument which comprises an air inlet mechanism, a liquid nitrogen input mechanism, a PID controller, a multi-stage cold trap and a multi-way valve, the air inlet mechanism is communicated with the multi-stage cold trap through the first pressure controller; the liquid nitrogen input mechanism is communicated with the multi-stage cold trap through an electromagnetic valve group and is controlled by a PID (Proportion Integration Differentiation) controller; the multi-stage cold trap is communicated with a multi-way valve, the multi-way valve is connected with an exhaust channel, and the exhaust channel is provided with an exhaust electromagnetic valve; the multi-way valve is respectively connected with a carrier gas input channel for inputting GC carrier gas and a carrier gas output channel for bringing the VOC sample to an external analysis instrument by the GC carrier gas; a temperature measuring module for monitoring tempera