Intelligent measurement instrument as information access tool is a set of multiple categories, multi-disciplinary technology in one complex organism. With the rapid development of test technology, computer technology and LSI technology, modern intelligent measurement instrument not only for functionality, performance, accuracy, and indicators have become increasingly demanding, but also for system reliability, maintainability requirements are more to be higher. Therefore, it requires measuring instruments with complete built-in test (build intest, BIT) function as well as the ability to self-regulation and compensation to the measuring instrument system itself has the ability to test, diagnose and fault localization and adaptation to the environment, temperature and changes in component performance capabilities.
However, the intelligent measurement instrument to have these tests, diagnostics and an adjustment, compensation capability, the entire measuring instrument must be monitored operating state, then the state of the nodes are analyzed and processed, thus further fault location or adjust the compensation. These states include the ambient temperature as well as the critical circuit nodes of the circuit board voltage, current, power, etc., as are analog, so often refer to these observations distributed nodes on the circuit board for the analog nodes. Visible detection of intelligent measurement instruments work environment as well as the key node analog intelligent built-in test and measurement instruments regulating the premise and basis of compensation, but also an important part of intelligent measurement instrument design for testability, the need to take seriously.
Here's a serial bus based intelligent measurement instrument analog signal monitoring circuit node did not count thinking and design methods.
1. Analog signal monitoring node design principles
A typical circuit board usually consists of an analog monitor circuit node signal detection channel, a signal conditioning circuit, the multiplexer switches, the sample / hold circuit, A / D converter circuit and a processor interface and control logic, and the like, as shown in FIG.
Signal detection channel is mainly used for temperature, current, voltage and other analog detection circuit board of each probe point, usually used for different detection target different sensor, detector or associated circuitry to be tested signal into a constant current or voltage signal.
Signal conditioning circuitry is necessary to deal with in order to ensure firstly before A / D conversion accuracy in the analog input signal into the A / D converter to effectively filter out the impact of unnecessary signals, improve signal quality, improve signal to noise ratio, enhanced signal under anti-interference ability, to ensure compliance with the input signal A / D converter and impose its optimum conversion van with. Signal conditioning employed techniques usually involve increased Mi amplification, attenuation, filtering, rectification, detection signal conversion. Multi-way switch is to simplify the circuit and reduce the cost and ensure a plurality of analog nodes share the same A / D converter is designed to facilitate the realization of a converted analog Chong by software. MUX commonly used mechanical and electronic contacts two kinds, according to the number of channels is usually required, input mode (single-ended or differential input), high and low level, switching time and settling time, ask the maximum allowable path crosstalk error and control methods to be considered options.
When the high frequency analog input signal node, to reduce aperture errors A / D conversion is often designed using sample / hold circuit. The sample holder is typically based on the input signal range, the rate of change of the input signal, the sampling switching speed and sampling error allowable range selection. If the low frequency input analog signal, A / D conversion relatively fast enough or A / D integrated may be omitted when the sample holder is designed sample holder.
A / D converter full analog input channels of the key components used to convert analog signals into digital signals by the processor in order to carry out a series of follow-up treatment. A / D converters are many kinds of devices, select the resolution takes into account conversion accuracy, speed and power conversion and other indicators. In general, A / D converter bits should choose quantization error and quantization noise into account, such as changes in accordance with the scope and the A / D converter analog input signal of the circuit under test.
2. Based on the serial bus analog signal monitoring node design
Modern measuring instruments intelligence and performance increasing, the increasing use of software adjustment, calibration and compensation performance indicators, while more and more real-time monitoring of the entire instrument needs to work to improve the system cho reliability, so the demand for analog node number is growing. In addition, modern intelligent measuring instruments are rapidly to low power, low cost, small size, high performance, high speed direction, circuit integration is growing, more and more low-cost, smaller size, frequency, and the more to be higher. As a measuring instrument auxiliary support circuitry to minimize board space occupied in meeting the functionality and performance of the premise, to reduce the effects of electromagnetic interference on other circuits, etc., has been a constant pursuit of the goal of the designer. Visible, based on traditional analog parallel bus signal monitoring node design can not meet the need.
With the birth of the serial bus interface technology and continues to mature, its simple interface, high data transmission efficiency, flexibility, and its scalable interconnect capabilities in the field of electronics and testing makes rapid promotion and application areas. Compared to a parallel interface, a serial interface to reduce pin count, the count did not decrease the complexity of the interface, the electromagnetic radiation is reduced and volume.
Generally provide full duplex synchronous serial interface, the data in bit serial input-output units. Each component manufacturers have introduced based on the serial bus devices, more and more processors have begun to integrate the appropriate serial communication interface, and is compatible with a number of popular serial bus. Therefore, under the premise of accuracy, speed, strength and other indicators differentiate license, select the multi-channel and serial ADC has a sample holder and other serial devices to build an analog measuring instrument based on the serial bus node program is undoubtedly an ideal choice . Design shown in Figure 2 is based on such a serial bus emulator node circuitry.
In the intelligent measurement instrument, the analog node is typically distributed in the respective circuit boards and functional modules of the instrument, and each circuit board and the functional modules in turn may comprise a plurality of analog detection nodes.
To this end, the design is often choose to use one or more pieces of multi-channel serial A / D chip (such as AD's AD7812, etc.) constitute the analog input channels per board or function module according to the number of nodes in the simulation, and different circuits board or serial device function modules are mounted on the same serial bus, by the processor to select the appropriate analog input channels through the control bus and decoding logic and control of serial devices accordingly. Further, in a specific design, the serial bus can be used often also some auxiliary circuit design: such as the use of some serial D / A converter constituting the analog output channels, as required to produce the appropriate analog signal, the circuit board related calibration and compensation circuit; design articulated some serial E2PROM memory for storing calibration and compensation parameters related to the channel, and so on.
However, the intelligent measurement instrument to have these tests, diagnostics and an adjustment, compensation capability, the entire measuring instrument must be monitored operating state, then the state of the nodes are analyzed and processed, thus further fault location or adjust the compensation. These states include the ambient temperature as well as the critical circuit nodes of the circuit board voltage, current, power, etc., as are analog, so often refer to these observations distributed nodes on the circuit board for the analog nodes. Visible detection of intelligent measurement instruments work environment as well as the key node analog intelligent built-in test and measurement instruments regulating the premise and basis of compensation, but also an important part of intelligent measurement instrument design for testability, the need to take seriously.
Here's a serial bus based intelligent measurement instrument analog signal monitoring circuit node did not count thinking and design methods.
1. Analog signal monitoring node design principles
A typical circuit board usually consists of an analog monitor circuit node signal detection channel, a signal conditioning circuit, the multiplexer switches, the sample / hold circuit, A / D converter circuit and a processor interface and control logic, and the like, as shown in FIG.
Signal detection channel is mainly used for temperature, current, voltage and other analog detection circuit board of each probe point, usually used for different detection target different sensor, detector or associated circuitry to be tested signal into a constant current or voltage signal.
Signal conditioning circuitry is necessary to deal with in order to ensure firstly before A / D conversion accuracy in the analog input signal into the A / D converter to effectively filter out the impact of unnecessary signals, improve signal quality, improve signal to noise ratio, enhanced signal under anti-interference ability, to ensure compliance with the input signal A / D converter and impose its optimum conversion van with. Signal conditioning employed techniques usually involve increased Mi amplification, attenuation, filtering, rectification, detection signal conversion. Multi-way switch is to simplify the circuit and reduce the cost and ensure a plurality of analog nodes share the same A / D converter is designed to facilitate the realization of a converted analog Chong by software. MUX commonly used mechanical and electronic contacts two kinds, according to the number of channels is usually required, input mode (single-ended or differential input), high and low level, switching time and settling time, ask the maximum allowable path crosstalk error and control methods to be considered options.
When the high frequency analog input signal node, to reduce aperture errors A / D conversion is often designed using sample / hold circuit. The sample holder is typically based on the input signal range, the rate of change of the input signal, the sampling switching speed and sampling error allowable range selection. If the low frequency input analog signal, A / D conversion relatively fast enough or A / D integrated may be omitted when the sample holder is designed sample holder.
A / D converter full analog input channels of the key components used to convert analog signals into digital signals by the processor in order to carry out a series of follow-up treatment. A / D converters are many kinds of devices, select the resolution takes into account conversion accuracy, speed and power conversion and other indicators. In general, A / D converter bits should choose quantization error and quantization noise into account, such as changes in accordance with the scope and the A / D converter analog input signal of the circuit under test.
2. Based on the serial bus analog signal monitoring node design
Modern measuring instruments intelligence and performance increasing, the increasing use of software adjustment, calibration and compensation performance indicators, while more and more real-time monitoring of the entire instrument needs to work to improve the system cho reliability, so the demand for analog node number is growing. In addition, modern intelligent measuring instruments are rapidly to low power, low cost, small size, high performance, high speed direction, circuit integration is growing, more and more low-cost, smaller size, frequency, and the more to be higher. As a measuring instrument auxiliary support circuitry to minimize board space occupied in meeting the functionality and performance of the premise, to reduce the effects of electromagnetic interference on other circuits, etc., has been a constant pursuit of the goal of the designer. Visible, based on traditional analog parallel bus signal monitoring node design can not meet the need.
With the birth of the serial bus interface technology and continues to mature, its simple interface, high data transmission efficiency, flexibility, and its scalable interconnect capabilities in the field of electronics and testing makes rapid promotion and application areas. Compared to a parallel interface, a serial interface to reduce pin count, the count did not decrease the complexity of the interface, the electromagnetic radiation is reduced and volume.
Generally provide full duplex synchronous serial interface, the data in bit serial input-output units. Each component manufacturers have introduced based on the serial bus devices, more and more processors have begun to integrate the appropriate serial communication interface, and is compatible with a number of popular serial bus. Therefore, under the premise of accuracy, speed, strength and other indicators differentiate license, select the multi-channel and serial ADC has a sample holder and other serial devices to build an analog measuring instrument based on the serial bus node program is undoubtedly an ideal choice . Design shown in Figure 2 is based on such a serial bus emulator node circuitry.
In the intelligent measurement instrument, the analog node is typically distributed in the respective circuit boards and functional modules of the instrument, and each circuit board and the functional modules in turn may comprise a plurality of analog detection nodes.
To this end, the design is often choose to use one or more pieces of multi-channel serial A / D chip (such as AD's AD7812, etc.) constitute the analog input channels per board or function module according to the number of nodes in the simulation, and different circuits board or serial device function modules are mounted on the same serial bus, by the processor to select the appropriate analog input channels through the control bus and decoding logic and control of serial devices accordingly. Further, in a specific design, the serial bus can be used often also some auxiliary circuit design: such as the use of some serial D / A converter constituting the analog output channels, as required to produce the appropriate analog signal, the circuit board related calibration and compensation circuit; design articulated some serial E2PROM memory for storing calibration and compensation parameters related to the channel, and so on.