PID (Proportion Integration Differentiation) temperature control circuit applied to microorganism culture monitor

Abstract

The utility model discloses a PID temperature control circuit applied to a microbial culture monitor. The PID temperature control circuit comprises a PID controller and a PID control circuit, the PID controller is used for receiving target temperature, incubation frame bias temperature and PID control parameters issued by the upper computer, receiving temperature parameters, sent by the PID control circuit, of all incubation frames in real time, conducting PID operation on the temperature parameters, outputting PWM adjusting signals to the PID control circuit according to operation results, and adjusting the temperature of the incubation frames by changing the output quantity of the PID control circuit. And the output power of the heating component or the refrigerating component is adjusted. The three-state buffer can buffer and isolate signals, prevent noise from interfering with the PID controller, protect the sensitive PID controller from being damaged by a rear-end circuit, and prevent residual output signals of the PID controller from influencing turn-off logic. In emergency, the output of the PID controller is cut off according to the emergency stop signal, so that the power switch device is quickly closed, the power output of the temperature control load is stopped, and the emergency stop function is realized.

Description

TECHNICAL FIELD

[0001] The utility model relates to PID temperature control circuit, especially a kind of PID temperature control circuit applied to microorganism culture monitor. BACKGROUND

[0002] When microorganism culture monitor operates, the instrument is detected by incubation, agitation and continuous monitoring, to detect the kind, quantity and growth state of aerobic, facultative and anaerobic microorganisms in culture sample (usually blood and other sterile body fluids). In this process, temperature control accuracy, temperature fluctuation, temperature uniformity have great influence on the growth state of microorganisms in sample, often determine the accuracy of monitoring results.

[0003] In order to improve the accuracy and reliability of instrument detection results, the incubation temperature needs to be detected in real time, and the heating component is used to heat when the temperature is too low, and the refrigeration component is used to cool when the temperature is too high. Common heating components include heating tube, heating wire, heating film, etc.; Common refrigeration components include TEC semiconductor refrigeration sheet and auxiliary refrigeration fan; The electrical performance of these components is quite different, and the requirements of control circuit are also different.

[0004] At present, the temperature control circuit used in microorganism culture monitor uses MOSFET tube (metal oxide semiconductor field effect tube) to form a switch control circuit to execute the PWM adjustment amount output by the controller; Since MOSFET tube gate drive circuit is fixed, MOSFET tube opening and closing speed cannot be adjusted according to actual application, which cannot be matched with control signal frequency and access load electrical performance, leading to easy damage of switching device, or the need to limit the type of access load. At the same time, there are the following shortcomings:

[0005] 1. No output detection circuit, cannot monitor output current in real time, instrument cannot send alarm prompt information in time when temperature control system fails;

[0006] 2. Unable to turn off the power output of heating component and TEC refrigeration assembly in emergency;

[0007] 3. Without noise interference isolation, easy to cause damage of sensitive controller. SUMMARY

[0008] Therefore, the utility model aims at providing a kind of PID temperature control circuit applied to microorganism culture monitor, to improve the temperature control accuracy and temperature uniformity of microorganism culture monitor, reduce temperature fluctuation.

[0009] To achieve the above purpose, the utility model takes the following technical solutions:

[0010] The PID temperature control circuit for a microbial culture monitoring instrument described in this invention includes a PID controller (MCU, DSP) and a PID control circuit. The PID controller receives the target temperature, incubator bias temperature, and PID control parameters from the host computer, and receives the temperature parameters of each incubator from the PID control circuit in real time. It performs PID calculations on the temperature parameters and outputs a PWM adjustment signal (TTL signal level or CMOS signal level) to the PID control circuit based on the calculation results. By changing the output of the PID control circuit, the output power of the heating or cooling component is adjusted.

[0011] Furthermore, the PID control circuit includes a three-state buffer, a gate drive circuit, power switching devices (MOSFET, IGBT, SiC / GaN devices), a current detection circuit, a temperature acquisition circuit, and an output interface circuit;

[0012] The tri-state buffer control signal input terminal is connected to the output control terminal of the PID controller to receive the PWM adjustment signal output by the PID controller; the tri-state buffer control signal output terminal is connected to the input terminal of the gate drive circuit. The PWM adjustment signal is processed by the tri-state buffer and then output as a control signal after being level-converted by the gate driver, which controls the power switching device to be turned on or off, thereby controlling the connection or disconnection of the output interface circuit and the system power supply.

[0013] The conduction time of power switching devices is related to the duty cycle of the PWM signal. The larger the duty cycle, the longer the conduction time of the power switching devices, and the higher the average voltage / current of the load, thereby achieving linear regulation of the output power.

[0014] Furthermore, the current detection circuit is used to detect the current value of the output interface circuit and convert the current value into an analog signal to be output to the PID controller.

[0015] After the heating and cooling components (TEC cooling components and cooling fans, etc.) are connected to the output interface circuit, they form a loop with the system power supply through the current detection circuit and power switching device.

[0016] This utility model has the following advantages:

[0017] 1. The tri-state buffer can buffer and isolate signals, prevent noise interference to the PID controller, protect the sensitive PID controller from damage by the back-end circuit, and avoid residual PID controller output signals affecting the shutdown logic. In an emergency, the PID controller output is disconnected according to the emergency stop signal, so that the power switching device is quickly turned off, stopping the power output of the temperature-controlled load and realizing the emergency stop function.

[0018] 2. The gate drive circuit realizes the level conversion of the control signal, so that the control signal matches the drive voltage required by the power switching device; it adjusts the turn-on and turn-off speeds of the power switching device to match the control signal frequency and the electrical performance of the connected load, thereby reducing the power switching device losses, protecting the power switching device, extending the life of the power switching device, improving the system efficiency, and also reducing the impact of electromagnetic interference (EMI) and parasitic parameters, thus improving system stability.

[0019] 3. The current detection circuit detects the magnitude of the output current in real time and feeds it back to the PID controller. The PID controller judges the working status of the load based on the feedback current signal and uploads it to the host computer for further analysis and processing. This enables the instrument to monitor the working status of each component in the temperature control system in real time and issue alarm prompts in a timely manner when the temperature control system malfunctions.

[0020] 4. The output interface circuit is designed with freewheeling diodes and filtering devices. When the load is connected, the freewheeling diodes can prevent high voltage spikes from damaging the power switching devices during the switching process. During the power switching device's turn-off period, the freewheeling diodes can reduce voltage oscillations and electromagnetic noise. The filtering devices can stabilize the voltage output, suppress voltage surges, and improve circuit stability.

[0021] 5. This solution uses PID control of the cooling fan to adjust the airflow speed of the circulating gas in the incubator, which can be adjusted to control the temperature. When used for cooling control, it further improves the instrument's temperature control accuracy, temperature fluctuation and temperature uniformity. Attached Figure Description

[0022] Figure 1 This is a circuit block diagram of this utility model.

[0023] Figure 2 This is the schematic diagram of the PID control circuit described in this utility model. Detailed Implementation

[0024] The embodiments of this utility model will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of this utility model and provide detailed implementation methods and specific operation processes. However, the protection scope of this utility model is not limited to the following embodiments.

[0025] It should be noted that in the description of this utility model, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0026] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0027] like Figure 1 As shown, the PID temperature control circuit of the present invention applied to the microbial culture monitoring instrument includes a PID controller and a PID control circuit 1. The PID controller is used to receive the target temperature, incubator bias temperature and PID control parameters sent by the host computer (controller of the microbial culture monitoring instrument), and to receive the temperature parameters on each incubator sent by the PID control circuit 1 in real time. The received temperature parameters are used to perform PID calculation, and the PWM adjustment signal is output to the PID control circuit 1 according to the calculation result. By changing the output of the PID control circuit 1, the output power of the heating component or the cooling component is adjusted.

[0028] Beneficially or exemplaryly, such as Figure 1 As shown, the PID control circuit 1 includes a three-state buffer, a gate drive circuit, a power switching device, a current detection circuit, a temperature acquisition circuit, and an output interface circuit.

[0029] The tri-state buffer control signal input terminal is connected to the output control terminal of the PID controller to receive the PWM adjustment signal output by the PID controller; the tri-state buffer control signal output terminal is connected to the input terminal of the gate drive circuit. After the PWM adjustment signal is processed by the tri-state buffer and then level-converted by the gate driver, the output control signal is output to control the power switching device to turn on or off, thereby controlling the connection or disconnection of the output interface circuit and the system power supply.

[0030] The tri-state buffer serves two purposes: First, it buffers and isolates signals to prevent noise interference with the controller and protects the sensitive PID controller from damage by downstream circuitry; it also prevents residual PID controller output signals from affecting the shutdown logic. Second, in emergency situations, it can quickly cut off the signal path between the PID controller and the gate driver based on emergency stop signals (such as instrument fault protection signals, emergency stop button triggers, etc.), causing the power switching devices to quickly turn off and stop outputting power to the temperature-controlled load, thus realizing the system's emergency stop function.

[0031] The gate drive circuit converts the low-voltage / low-current PWM adjustment signal (signal level is TTL or CMOS level) output by the PID controller through a tri-state buffer into a high-voltage / high-current drive signal suitable for the power switching device, ensuring the power switching device is turned on or off. By changing the rise and fall rates of the signal level, the switching speed of the power switching device is increased. This is achieved by rapidly charging and discharging the gate capacitance of the power switching device through high-current drive capability, shortening the switching time, reducing power switching device losses (such as cross-conduction losses caused by the Miller effect), protecting the power switching device, extending its lifespan, and improving system efficiency. On the other hand, for loads with specific electrical performance and control signal frequencies, excessively fast switching speeds of the power switching device can lead to electromagnetic interference (EMI), increased switching losses, heat generation, and parasitic parameter effects. Therefore, it is necessary to select an appropriate switching speed based on the frequency of the control signal and the electrical performance of the connected load. The gate drive circuit in this solution can adjust the turn-on and turn-off speeds of the switching device separately by adjusting the resistance value of a specific resistor.

[0032] The current detection circuit is used to detect the magnitude of the output current in real time and feed it back to the PID controller. The PID controller judges the load working status based on the feedback current signal and uploads it to the host computer for further analysis and processing. This enables the host computer to monitor the working status of each component in the temperature control system in real time, and can issue alarm prompts in a timely manner when the temperature control system malfunctions.

[0033] The output interface circuit consists of a freewheeling diode and a filter. When an inductive load (such as a fan) is connected, the current of the power switching device is suddenly interrupted during switching, and the inductor generates a reverse high voltage (back electromotive force). The freewheeling diode provides a low-impedance loop, guiding the current back to the power supply or load, preventing the high-voltage spike from damaging the power switching device. During the power switching device's off-state, the freewheeling diode allows the energy stored in the inductor to continue flowing, preventing electromagnetic interference (EMI) and load vibration caused by sudden current changes, and reducing system voltage oscillations and electromagnetic noise. The filter's main function is to stabilize the voltage output, suppress voltage surges, and improve circuit stability. Specifically, such as... Figure 2As shown, VSYS is the operating voltage of the external load of the temperature control system; VDD is the operating voltage of digital circuits such as the PID controller, matched with TTL or CMOS level signals; VCC is the operating voltage of the gate driver, matched with the driving voltage of the power switching device Q1 (MOSFET, IGBT, SiC / GaN device); U1 (74HC245) is a tri-state buffer that can shut off the PWM adjustment signal of the PID controller (MCU, DSP) input from the CH2 port according to the emergency stop signal input from the CH1 port; U2 (IVCR1801SR) is the gate driver, which can... By adjusting the resistance values ​​of R2 and R3, the rise and fall rates of the signal level can be changed, thereby adjusting the turn-on and turn-off speeds of the power switch Q1. U3 (NSM2012-10U3R-DSPR) is a current sensor that can detect the current output to J1 (output interface circuit), convert the detected current value into an analog signal, and output it through the CH3 port. D1 is a freewheeling diode, and C1 is a filter capacitor. The capacitor C1 can be adjusted according to the specific application. Of course, an RC filter, LC filter, or multi-stage capacitor filter composed of multiple components such as resistors or inductors can be used to replace the filter capacitor.

[0034] The PID controller receives a PWM adjustment signal (TTL or CMOS level) through port CH2. After being processed by the tri-state buffer U1, the PWM adjustment signal is input to the gate driver U2. U2 performs level conversion on the PWM adjustment signal, converting the TTL or CMOS level signal into a level signal that matches the driving voltage of the power switching device Q1, thus controlling the on or off state of Q1. When Q1 is on, the load connected to J1 forms a loop with the VSYS power supply through Q1 and U3. When Q1 is off, the load connected to J1 is disconnected from the VSYS power supply. The on-time of Q1 is related to the duty cycle of the PWM adjustment signal. The larger the duty cycle, the longer the on-time of Q1, and the higher the average voltage / current output of J1, thereby achieving linear regulation of the output power. After filtering by C1, the output power is controlled and stable.

[0035] Finally, it should be emphasized that the above description is merely a preferred embodiment of this utility model and is not intended to limit this utility model. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A PID temperature control circuit for use in a microbial culture monitoring instrument, characterized in that: It includes a PID controller and a PID control circuit; the PID controller is used to receive control commands sent by the host computer and receive the temperature parameters on each incubation rack sent by the PID control circuit in real time, perform PID calculation on the temperature parameters, and output a PWM adjustment signal to the PID control circuit according to the calculation result, thereby adjusting the output power of the heating or cooling component by changing the output of the PID control circuit. The PID control circuit includes a three-state buffer, a gate drive circuit, a power switching device, a current detection circuit, a temperature acquisition circuit, and an output interface circuit. The three-state buffer control signal input terminal is connected to the output control terminal of the PID controller, and is used to receive the PWM adjustment signal output by the PID controller; The output terminal of the three-state buffer control signal is connected to the input terminal of the gate drive circuit. The PWM adjustment signal is processed by the three-state buffer and then output as a control signal after being level-converted by the gate driver. This control signal controls the power switching device to be turned on or off, thereby controlling the connection or disconnection of the output interface circuit with the system power supply. The current detection circuit is used to detect the current value of the output interface circuit and convert the current value into an analog signal to be output to the PID controller.

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