Method for automatically determining type of DDC output signal and monitoring DDC output signal in real time

Abstract

The invention discloses a method for automatically determining the type of a DDC output signal and monitoring the DDC output signal in real time. An MCU outputs a digital quantity signal VD, a DAC unit circuit converts the digital quantity signal VD into an analog signal VA, and a voltage or current output unit converts the VA into the default output signal type and value of the DDC; the MCU determines whether the subordinate equipment is short-circuited or not, if the subordinate equipment is not short-circuited and the detection voltage value is not smaller than or equal to a threshold value, the subordinate equipment is in a current input type, otherwise, the subordinate equipment is in an open circuit or not for outputting detection voltage, and if the output current at the moment is smaller than or equal to a current threshold value, no subordinate equipment is connected, otherwise, the subordinate equipment is in voltage type input; the DDC outputs a normal control voltage or current value according to a detection result, and a voltage detection circuit dynamically detects a voltage value detection value VS at the two ends of the RS and feeds back the voltage value detection value VS to the MCU; the MCU is used for comparing and judging with the VS by combining the set signal output type and value; and outputting a port state, and performing DDC communication reporting. The working mechanism is clear, the intelligent degree is high, and signal errors can be avoided.

Description

Technical Field

[0001] This invention application belongs to the field of automated measurement technology, specifically relating to a method for automatically determining the type of DDC output signal and monitoring it in real time. Background Technology

[0002] With the continuous popularization of automation technology, DDC (Direct Digital Control) is widely used in building intelligence, chemical production processes, food processing and real-time pH adjustment of water treatment plants. The output of DDC is usually 0-5V or 0-10V voltage type and 0-20mA or 4-20mA current type.

[0003] Typically, for a "field controller" or DDC, the sampling resistor value is ≥1kΩ when the signal input is configured as voltage type, and ≤250Ω when the signal input is configured as current type. Regardless of whether the signal is voltage or current, the input port voltage is limited to 12V. The short-circuit current of a DDC outputting a voltage signal is typically ≤12mA, and the open-circuit voltage of a DDC outputting a current signal is ≤12V. The signal input type of a DDC or field controller is usually set to current type by default.

[0004] The DDC output signal is connected to a field controller, such as various valve actuators (controlling valve opening), frequency converters (controlling motor speed), or cascaded DDCs to achieve process automation control. Correspondingly, the input signals of the field controller are typically 0-5V or 0-10V voltage and 0-20mA or 4-20mA current. That is, there is a "signal type" matching issue between the two. If the signal types used in the "handshake" between the two are inconsistent, it will lead to serious consequences such as inaccuracy or loss of control. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a method for automatically determining and monitoring the output signal type of a DDC in real time. This method can avoid signal mismatch between the DDC and the field control regulator. The field control regulator connects to the DDC using a default input method, and the DDC automatically determines its own signal output type. It also monitors in real time whether short circuits or open circuits in the signal link are caused by objective reasons such as line aging or construction damage during operation.

[0006] A method for automatically determining and monitoring the output signal type of a digital signal generator (DDC) in real time includes connecting an MCU unit to a DAC (PWM) unit, and the MCU outputting a digital signal V. D Converted from DAC (PWM) to analog signal V A The DAC (PWM) unit outputs signal V. AConnected to a voltage or current output unit, the voltage or current output unit signal V P With the sensing resistor R S One end is connected to one end of the voltage detection circuit, R S The other end outputs voltage V O Connect to the other end of the voltage detection circuit, and to the external or next-stage sampling input port resistor R. L The connection and voltage detection circuit unit respectively receive V P and V O After processing, the voltage detection circuit unit outputs a signal V. S It is connected to or controlled by an MCU unit, and the MCU unit is connected to a voltage or current output unit to control the output signal type as a voltage signal or a current signal.

[0007] The voltage detection circuit unit includes a sophisticated ADC conversion circuit or a simple voltage comparator circuit, for R S The voltage value at one or both terminals is sampled and converted, and the magnitude of the output signal value V is... S Provides criteria for the MCU unit, which determines the type and magnitude of the current output signal based on V. S The comparison process determines whether the downstream equipment is connected, the signal input type of the downstream equipment, and the dynamic conditions such as open circuits or short circuits that may occur in the connection lines during operation.

[0008] The voltage detection circuit has a built-in sampling resistor R. S Specifically, the voltage sampling resistor R SV and current sampling resistor R SI The switching state is controlled by the MCU. Through a pair of electronic or mechanical switching switches, the MCU controls the voltage and current output type while simultaneously switching the sampling signal V of the voltage detection circuit unit. P Indicates the direction of voltage or current.

[0009] The DAC (PWM) unit includes a DAC unit embedded in the MCU, an external DAC chip circuit that is independent but controlled by the MCU, a DAC-type circuit consisting of an active or passive first-order or second-order RC filter after the MCU outputs the PWM signal, and a dedicated chip that directly converts the PWM signal into DC voltage.

[0010] The voltage or current output unit includes 0-5V and 0-10V voltage signal output circuits used in DDC, and 0-20mA and 4-20mA current signal output circuits. The circuit module is controlled by MCU, and the MCU controls its signal output type and value.

[0011] The MCU (Microcontroller Unit / Single-Chip Microcomputer) mentioned includes various models of MCUs ranging from 8-bit to 32-bit, and is the core device of the original DDC.

[0012] The voltage detection circuit unit includes an 8-bit to 24-bit ADC conversion circuit with dual-channel differential sampling or more independent sampling inputs, for V P and V O Sample and convert to digital quantity V S Or a simple voltage comparator circuit, for V O Perform a constant value comparison and output V S Signal.

[0013] Compared with the prior art, the beneficial effects of this invention are: by optimizing the DDC circuit design, this invention embeds a detection resistor R within the output voltage / current output unit. S The MCU samples and feeds back the voltage value across the detection resistor. Combined with the established identification program, the MCU automatically identifies the input type of the downstream device, determines whether the connection line is open or short-circuited, and dynamically monitors whether the signal transmission process is normal. It has the advantages of fast identification speed and ensuring consistency with the signal type of the downstream device. By constructing an internal closed-loop mechanism, the existing DDC becomes a highly intelligent DDC. Attached Figure Description

[0014] Figure 1 This diagram illustrates a method for automatically determining and monitoring the output signal type of a DDC in real time.

[0015] Figure 2 This is a flowchart of a method for automatically determining and monitoring the output signal type of a DDC in real time.

[0016] Figure 3 This is an extended diagram of a method for automatically determining and monitoring the output signal type of a DDC in real time. Detailed Implementation

[0017] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0018] A method for automatically determining the output signal of a digital signal generator (DDC) includes connecting an MCU unit to a DAC (PWM) unit, and the MCU outputting a digital signal V. D Converted from DAC (PWM) to analog signal V A The DAC (PWM) unit outputs signal V. A Connected to a voltage or current output unit, the voltage or current output unit signal V P With the sensing resistor R S One end is connected to one end of the voltage detection circuit, R S The other end outputs voltage VO Connect to the other end of the voltage detection circuit, and to the external or next-stage sampling input port resistor R. L The connection and voltage detection circuit unit respectively receive V P and V O After processing, the voltage detection circuit unit outputs a signal V. S It is connected to or controlled by an MCU unit, and the MCU unit is connected to a voltage or current output unit to control the output signal type as a voltage signal or a current signal.

[0019] MCU outputs digital signal V D The signal is converted into an analog signal V by the DAC (PWM) unit circuit. A The voltage or current output unit will output V A The signal is converted to the default output signal type and value of the DDC, such as a current output signal of 0mA. After power-on, the MCU, in accordance with the established program, first uses the "detector current" method to determine whether the downstream device is in a short-circuit state. If it is not in a short-circuit state, and the detector voltage value is not greater than a threshold, it is considered that the downstream device is a current input type. Otherwise, it outputs the "detector voltage" to determine whether the downstream device is in an open-circuit state. If the output current at this time is less than or equal to a current threshold, no downstream device is connected; otherwise, it is a voltage input type.

[0020] Based on the detection type result, the DDC outputs a normal control voltage or current value, which is dynamically detected by the voltage detection circuit using the built-in detection resistor R. S The voltage value at both ends, the obtained detection value V S The feedback is sent to the MCU for processing. The MCU combines the predetermined signal output type and value with V. S By comparing and judging, the output can be dynamically tracked, thus achieving full-process output monitoring.

[0021] The DDC can display the four states of the output port—no-load, short-circuit, voltage type, and current type—locally or report them to higher-level devices.

[0022] This circuit uses a voltage detection circuit to detect the voltage value at one or both ends of a sampling resistor, or the current value therein, thereby automatically determining the DDC output signal type and dynamically monitoring the load status. It has significant advantages such as a clear working mechanism, high level of intelligence, and avoiding signal errors caused by inconsistencies between the signal output type and the input type of downstream devices.

[0023] like Figure 1 As shown, the input port resistance value of the field control regulator or lower-level DDC is defined as R. L The internal sensing resistor of the DDC is R. S .

[0024] DDC, including the digital signal V output by the MCU D Converted from DAC (PWM) to analog signal V A The DAC (PWM) unit outputs signal V. A Connected to a voltage or current output unit, which is controlled by the MCU, the voltage or current output unit defaults to current output mode with an output value of 0mA (0V). The voltage or current output unit internally outputs a signal V. P With R S One end is connected to one end of the voltage detection circuit, R S The output voltage V at the other end O Connect to the other end of the voltage detection circuit, and to R L The connection and voltage detection circuit unit respectively receive V P and V O The conversion process is performed, and the output signal V is obtained. S Connected to an MCU unit, the MCU unit controls its sampling rate and converts the sampled value V into a digital representation of the sampled value. S With a given value V D The comparison is used to determine whether the output port is in an open-circuit or short-circuit state, and whether the signal type is a voltage signal or a current signal.

[0025] In the DDC, the MCU unit output signal is converted by DAC (PWM). Simultaneously, the MCU unit puts the voltage or current output unit into current output mode, outputting the corresponding "detection current" (e.g., 1mA). The MCU then activates the voltage detection circuit to detect V. O The specific value is detected; if it is less than or equal to a voltage threshold V... TH0 (e.g., 10mV) indicates that the output port is in a "short-circuit state". If it is not greater than a voltage threshold V, TH0 (e.g., 500mV) indicates that the downstream device is a "current-type" input. Further calculations using Ohm's law can be made to determine R under current transmission mode. L The specific value R LI If greater than or equal to V TH0 The MCU unit puts the voltage or current output unit into voltage output mode and outputs the corresponding "detection voltage" (e.g., 10V). The MCU then activates the voltage detection circuit to detect the voltage. P With V O Detect and calculate the difference ΔV RS Divide by R S The value of the current i flowing through it is obtained. O Size, if less than or equal to a current threshold I TH0 (e.g., 50uA) indicates that the output port is in an "open circuit" state; otherwise, the downstream device is of the "voltage input" type. O value divided by i O It is worth noting that R is under voltage transmission mode. LThe specific value R LV .

[0026] See attached flowchart Figure 2 .

[0027] Taking the reference (but not limited to) values ​​in parentheses above as an example, when the DDC automatically detects the input port of the field control regulator or the lower-level DDC in "current input" mode, the maximum input (sampling) resistance value is 500Ω and the minimum value is 10Ω; when in "voltage input" mode, the maximum is 200kΩ, which is sufficient to meet the needs of product cascading projects.

[0028] Furthermore, by employing a closed-loop detection method that detects both current "transformation" and voltage "transformation," a wider range of R can be detected. L Identification.

[0029] The aforementioned "detection" of current or voltage is all within the safe range of voltage and current of the downstream equipment and is completed within a short time (such as 1ms), and will not cause any harmful effects on the downstream equipment.

[0030] Through the above steps, the DDC displays the open circuit, short circuit, voltage type, or current type signal status of the output terminal locally in the form of status indicator lights or digital tube displays, or further transmits these status information to the upper-level equipment.

[0031] Since R of the lower-level device has already been calculated. L During normal signal transmission, the DDC outputs information based on the current voltage or current characteristics and specific values, combined with the corresponding R... LV or R LI This enables online dynamic detection. Taking current transmission as an example, the downstream device R... L The current impedance is 250Ω, and the current output current is 10mA. The MCU samples V through the voltage detection circuit. O The value should be 2.5V, once V O A value less than a threshold (e.g., 10mV) indicates a short circuit in the connection; once V... O A value greater than a threshold (e.g., 10V) indicates an open circuit in the connection; set another "error threshold" (V). TE (e.g., 5%), V O If the value is within this range [2.5 ± (2.5 × 5%)], it indicates that the signal transmission is normal. Otherwise, the signal transmission is affected by interference or abnormalities such as line aging, and a corresponding alarm signal will be issued and the output signal value will be reduced to zero.

[0032] Voltage and current output circuits come in various forms, but their basic principles are largely the same. A typical example can be found in CN202211004495.6. In order to achieve "detection" and "monitoring", a detection resistor RS needs to be set inside the DDC.

[0033] like Figure 3 As shown, it includes the sensing resistor R. S The positive input terminal of operational amplifier U1 receives the input voltage control, and its output terminal is connected to the base of NPN transistor T1 through resistor R1 for current limiting. The emitter of T1 is connected to the left end of the "two-to-one" selector switch J1, and to the voltage output circuit sensing resistor R. SV Connection, R SV One end of the selector switch J2 is connected to the left end, and the other end is connected to resistor R2. The other end of R2 is connected to R3, which is connected to the - terminal of U1. The other end of R3 is connected to ground. The collector of T1 is connected to one end of resistor R4, and the other end of R4 is connected to a 24V (or 15V, etc.) power supply. The common terminal of the "two-to-one" selector J2 serves as the output terminal, outputting the voltage signal V. O Clearly, U1, R1, T1, R SV R1, R2, and R3 form a non-inverting amplifier circuit with a gain of 1 + (R2 / R3). Due to the virtual characteristics of the op-amp, the - and + terminals of U1 are at the same potential. If the input control voltage Vin ranges from 0 to 3.0V, and R3 = 1kΩ, then when Vin = 3.0V, the output voltage is 10V, and R2 = 2.33kΩ can be calculated. The common terminal V of J1... P As the input terminal of the voltage detection circuit, if it is a voltage output type, J1 and J2 both turn to the left, V O Output voltage value, V P and V O As the differential output terminal of the voltage detection circuit, it is used to detect R. SV The current value in R. SV Series connected in voltage output V O Before the feedback loop (R2 and R3), it will not affect the voltage output accuracy. SV The current in the output is the actual voltage i. O With feedback current i b The sum of i b Strictly proportional to the output voltage, therefore the voltage type and actual output current i O The specific value can be obtained through simple calculation. That is, when the voltage type output is applied, judging the magnitude of this current value can enable a "detective" function to check whether the circuit is open and to monitor in real time whether the voltage output is normal.

[0034] The collector of T1 is connected to one end of R4 and to the positive terminal of U2. The other end of R4 is connected to 24V. The negative terminal of U2 is connected to the emitter of T2 and to one end of R5. The other end of R5 is connected to 24V. The output terminal of U2 is connected to one end of R6. The other end of R6 is connected to the base of T2. The collector of T2 is connected to the right side of J1 and to R... SI One end is connected, RSI The other end is connected to the right side of J2. The MCU causes J1 and J2 to simultaneously turn to the right to connect the output current. Obviously, U2, R6, and T2 are non-inverting follower circuits, and the output current of T2 is i. O The value depends on the ratio of the voltage across R5 to the voltage across R5. Meanwhile, the voltage at the + terminal of U2 depends on the voltage across R4. The voltages at the + and - terminals of the op-amp's virtual characteristic U are equal, meaning the voltages across R4 and R5 are equal. The current in R4 is equal to the current in R3. The output current is Vin / R3, thus achieving a linear conversion from input control voltage to output control current.

[0035] J1 and J2 can be selected from dual-channel "2-to-1" analog transfer switches, such as CD4052, TS5A3159, etc.

[0036] R SI Using a smaller value (e.g., 5Ω) in series in the current output circuit will not affect the upper limit of the output voltage range. During the "current detection" phase, the MCU detects V through a single-channel voltage detection circuit. O Size; during the current-type signal output operation phase, V is detected respectively. P and V O And calculate the difference, then divide by R. L The actual output current value i is obtained. O It compares and judges the output current with the theoretical value, similar to voltage signal transmission, to determine whether the connection line is normal, and realizes dynamic monitoring during current signal transmission.

[0037] In the above embodiments, details such as input port protection circuits are omitted in order to briefly describe the basic principles.

Claims

1. A method for automatically determining and monitoring the output signal type of a digital digital converter (DDC) in real time, characterized in that, Includes the following steps: Step S1: The MCU outputs a digital signal V D The signal is converted into an analog signal V by the DAC unit circuit. A The voltage or current output unit will output V A The signal is converted to the default output signal type and value of the DDC; Step S2: After power-on, the MCU, in conjunction with the established program, first uses the "detector current" method to determine whether the downstream device is in a short-circuit state. If it is not in a short-circuit state, and the detector voltage value is not greater than a threshold, it is considered that the downstream device is a current input type. Otherwise, it outputs the "detector voltage" to determine whether the downstream device is in an open-circuit state. If the output current at this time is less than or equal to a current threshold, no downstream device is connected; otherwise, it is a voltage type input. Step S3: Based on the detection type result, the DDC outputs a normal control voltage or current value, which is dynamically detected by the voltage detection circuit using the built-in detection resistor R. S The voltage value at both ends, the obtained detection value V S Feedback is sent to the MCU for processing; Step S4: The MCU combines the predetermined signal output type and value with V S By comparing and judging, the output can be dynamically tracked and monitored throughout the entire process. Step S5: The DDC displays the four states of the output port—no-load, short-circuit, voltage type, and current type—either locally or communicates and reports them to a higher-level device.

2. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, In step S1, the DAC unit outputs signal V A Connected to a voltage or current output unit, the voltage or current output unit signal V P With the sensing resistor R S One end is connected to one end of the voltage detection circuit, R S The other end outputs voltage V O Connect to the other end of the voltage detection circuit, and to the external or next-stage sampling input port resistor R. L The connection and voltage detection circuit unit respectively receive V P and V O After processing, the voltage detection circuit unit outputs a signal V. S It is connected to or controlled by an MCU unit, and the MCU unit is connected to a voltage or current output unit to control the output signal type as a voltage signal or a current signal.

3. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, In step S3, the voltage detection circuit unit includes an 8-bit to 24-bit ADC conversion circuit with dual-channel differential sampling or more channels of independent sampling input, for V P and V O It samples and converts the voltage to a digital value VS; it also includes a simple voltage comparator circuit for V. O Perform a constant value comparison and output V S Signal.

4. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, In step S4, the MCU dynamically tracks the output by determining whether the downstream device is connected, the signal input type of the downstream device, and the dynamic situation of open circuit or short circuit that may occur in the connection line during operation, so as to realize the output monitoring of the whole process.

5. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, The voltage detection circuit has an embedded sampling resistor R. S Specifically, the voltage sampling resistor R SV and current sampling resistor R SI The switching state is controlled by the MCU. Through a pair of electronic or mechanical switching switches, the MCU controls the voltage and current output type while simultaneously switching the sampling signal V of the voltage detection circuit unit. P Indicates the direction of voltage or current.

6. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, The DAC unit includes a DAC unit embedded in the MCU, an external DAC chip circuit that is independent but controlled by the MCU, a DAC-type circuit consisting of an active or passive first-order or second-order RC filter after the MCU outputs a PWM signal, and a dedicated chip that directly converts the PWM signal into DC voltage.

7. The method for automatically determining and real-time monitoring the DDC output signal type according to claim 1, characterized in that, The voltage or current output unit includes a 0-5V or 0-10V voltage signal output circuit and a 0-20mA or 4-20mA current signal output circuit used in the DDC. The circuit module is controlled by the MCU, which controls the signal output type and value.

8. The method for automatically determining and real-time monitoring the output signal type of a DDC according to claim 1, characterized in that, The MCUs mentioned are available in models ranging from 8-bit to 32-bit.

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