DE4200935C1 - Single power supply for multiple micro controlled A=D converters - has isolating switch stages coupled to output of DC=DC converter for connection to multiple A=D converters and amplifiers - Google Patents

Abstract

Each transducer channel has a transmitter (11,12) coupled to an analogue amplifier (21,22,2n) that provide inputs to A/D converter stages (31,32,3n). Digital outputs are processed by microprocessors (51,52,5n). The common supply voltage for operations of the converters and amplifiers is provided by DC to DC isolated converter. The reference voltage on the output of the converter is coupled to isolating switches (41,42,4n). Auxiliary energy supply capacitors (711,712) are connected between the supply lines. USE/ADVANTAGE - Measurement acquisition in automation systems. Avoids balancing currents flowing through connection of reference potentials to analogue parts and digital parts during conversion.

Description

The invention relates to a circuit arrangement for the power supplier of the analog functional parts of several microcomputer controlled Analog-digital converter and analog value preprocessing modules from a common operating voltage source.

In modern process automation, measured value acquisition systems are steme needs, to which ever higher requirements regarding the accuracy and the measurable measured values per unit of time are put. Micro-computer controlled systems are used sets, in which the analog measurands via transmitter and corresponding analog value preprocessing modules on the Ana log input of an analog-digital converter, which after Call by the microcomputer the analogue size into a digital value that the microcomputer then uses for further processing is available.

The accuracy of the analog-to-digital conversion is particularly important more integrated, higher resolution and faster analog Digital converters and a. by the applied operating voltages and Reference potentials affected. Most analog-to-digital converters  Circuits require an exact match of the Reference potential for the analog with the reference potential for the digital part.

In the analog-to-digital converter circuit, there are counters or evaluation registers contain the analog input variable over a Compare reference. The comparison between the input and the Reference is made by a comparator, the reference of which is the reference potential for the analog part. The control of the reference steps takes place internally in an analog-to-digital converter or from the microcomputer controlled based on the reference potential of the digital part.

The component manufacturer of an analog-digital converter applied the electrical connection between the reference potential for the analog part and the reference potential for the digital part Part by topography sections on the analog-digital converter and by the power supply conditions, resulting in the Analog part and the digital part of the analog-to-digital converter electrically isolated power supply devices, e.g. B. DC / DC converters that need to be supplied to compensating currents and associated potential differences via the connection of the Avoid reference potentials of the analog part and the digital part.

From Electronics Information No. 3-1989, pp. 68, 75-76, Figure 5 a circuit arrangement with several analog-digital converters known in which the analog-to-digital converter with a microcomputer are connected.

In systems that contain multiple analog-to-digital converters, which with an assigned or one for all analog Digital converters are common microcomputers consequently all analog parts of the analog-digital converter and associated analog preprocessing modules from Power supply for the digital parts and microcomputer galvanic Assign separate power supply devices to reference potential loops  via the connections of the analog-digital converter to avoid, which greatly affect the conversion accuracy.

The assignment of a galvanically isolated power supply device  for each analog part in data acquisition systems with several Analog-digital converters have cost-effective and constructive after parts by a proportionate for the power supplies high space requirements must be provided.

The invention seeks to remedy this. Object of the invention is therefore a circuit arrangement for the power supply of the analog functional parts of several microcomputer controlled analog Digital converters and analog value preprocessing modules to create a common operating voltage source, with wel cher equalizing currents via the connections of the reference potentials the analog parts and the digital parts of the analog-to-digital converter avoided during the conversion and which none galvanically isolated power supply devices for the analog parts the analog-to-digital converter has.

To solve this problem, a circuit arrangement for Power supply for several micro-computer controlled analog-digital Specified converter from a common operating voltage source, which is characterized in that between the common Operating voltage source and the power supply inputs of the analog functional parts of the microcomputer controlled analog digi tal converter and analog value preprocessing modules each micro-computer controlled all-pole disconnectors are arranged and the power supply inputs of the analog functional parts of the Analog-digital converter and analog value preprocessing modules assigned auxiliary power sources are upstream, which the Power supply for the analog functional parts of the analog-digital Converter and analog value preprocessing modules at each Open the all-pole disconnector.

There are micro-controlled all-pole disconnectors preferably fast-acting electronic switches used.  

In the following the principle of operation of the Invention described circuit arrangement.

The invention is based on the knowledge that the ver binding of the analog with the digital reference potential the accuracy of the conversion only then affect if these flow during the conversion. Equalization currents before and after the conversion affect the Conversion accuracy is not.

At the time when there is no conversion, this is the case associated micro-computer-related analog-digital converter controlled all-pole disconnector closed. About the reference spo potential flowing equalizing currents are, as described, during this time without influence.

If the microcomputer has an analog-to-digital converter Requests measured value, the relevant all-pole disconnector opened shortly before by the microcomputer, whereby the analog Functional part of the analog-digital converter and the analog value Preprocessing assembly from the DC power supply be separated. After the conversion is complete, the Microcomputer in the relevant all-pole disconnector again the closed state.

During the conversion, this is the equalizing current leading circuit by opening the all-pole disconnector interrupted and the conversion accuracy is not thereby adversely affected.

The upstream aids take over during the conversion Energy sources power the analog functional part of the Analog-digital converter and the analog value Preprocessing assembly.

In a preferred embodiment of the invention are as Auxiliary energy sources used energy storage components  with each closed all-pole disconnector from the ge common energy source. Capacitors are preferably used as energy storage components used, at each pole of the operating voltage supply one capacitor is connected to one terminal and the other terminals of the capacitors are at the reference potential.

The invention is to follow in more detail using an exemplary embodiment are explained.

The figure shows a basic circuit diagram of a measured value acquisition system with n measured value acquisition levels. Each measured value acquisition level consists of a transmitter 11 , 12 , 1 n, an instrumentation amplifier as an analog value preprocessing module 21 , 22 , 2 n, an analog-digital converter 31 , 32 , 3 n, a microcomputer 51 , 52 , 5 n, one Microcomputer-controlled all-pole disconnector 41 , 42 , 4 n and capacitors 711 , 712 , 721 , 722 , 7 n1, 7 n2 used as auxiliary energy sources. The operating voltage supply of the microcomputers 51 , 52 , 5 n and digital functional parts of the analog-digital converters 31 , 32 , 3 n of all measured value acquisition levels takes place from the same operating voltage source.

The common operating voltage supply for the analog functional parts of the analog-digital converter 31 , 32 , 3 n and the instrumentation amplifier as analog value preprocessing modules 21 , 22 , 2 n takes place in an electrically isolated manner via a DC / DC isolating converter 6 . The bipolar operating voltage provided by the DC / DC isolating converter 6 is connected via the microcomputer-controlled all-pole isolating switches 41 , 42 , 4 n to the operating voltage inputs of the analog functional parts of the analog-digital converters 31 , 32 , 3 n and the instrumentation amplifier 21 , 22 , 2 n connected. The reference potential at the output of the DC / DC isolating converter 6 is connected to the reference potential of the analog modules AGND via a connection of the micro-computer-controlled all-pole isolating switches 41 , 42 , 4 n.

Furthermore, capacitors 711 , 712 , 721 , 722 , 7 n1, 7 n2 are provided as auxiliary energy sources, a capacitor having a terminal being connected to each pole of the analog operating voltage supply and the other terminals of the capacitors being connected to the reference potential for the analog modules AGND lie. The analog and digital reference potentials are connected to each other at the analog-to-digital converters 31 , 32 , 3 n as required.

If the microcomputer 51 , 52 , 5 n have no measured value request, no conversion takes place by the analog-digital converter 31 , 32 , 3 n and the microcomputer-controlled all-pole isolating switch 41 , 42 , 4 n are closed. The capacitors 711 , 712 , 721 , 722 , 7 n1, 7 n2 are charged and the analog functional parts of the analog-digital converter 31 , 32 , 3 n and the instrumentation amplifier 21 , 22 , 2 n are directly connected to the through DC / DC isolating converter 6 provided bipolar operating voltage connected ver. The equalizing currents flowing over the connections between the analog and digital reference potential have no effect on the measured value.

The mode of operation of the circuit arrangement in the event of a measurement value request, for example by the microcomputer 51 , is described below.

It is assumed that the analog measured value is present at the analog input of the analog-digital converter 31 .

First, the all-pole disconnector 41 is opened by the microcomputer 51 . The conversion is then triggered by the microcomputer 51 in the analog-digital converter 31 . After the conversion is complete and the digitized measured value is available, the all-pole disconnector 41 is closed again by the microcomputer 51 .

During the measured value conversion, the analog functional part of the analog-digital converter 31 and the instrumentation amplifier 21 are separated from the common operating voltage supply by the DC / DC isolating converter 6 . The voltage supply of these analog modules is taken over during the conversion by the charge on the capacitors 711 , 712 . The capacitors 711 , 712 are dimensioned in accordance with the current requirement of the analog modules to be supplied. After completion of the conversion and closing of the all-pole disconnector 41 , the capacitors 711 , 712 from the common operating voltage source 6 are recharged.

During the conversion, due to the interruption of the the reference potential of the leading circuit via the connection between the analog and digital reference potential none Equalizing currents flow, causing the expected conversion accuracy is achieved.  

List of reference symbols

11 , 21 , 1 n transmitter
21 , 22 , 2 n analog value preprocessing modules for instrumentation amplifiers
31 , 32 , 3 n analog-digital converter
41 , 42 , 4 n micro-computer controlled all-pole disconnector
51 , 52 , 5 n microcomputer
6 common operating voltage source DC / DC isolating converter
711, 712, 721, 722, 7 n1, 7 n2 capacitors, energy storage components used as auxiliary energy sources
AGND reference potential for analog modules
DGND reference potential for digital assemblies
+ U, -U Poles of the operating voltage supply

Claims (4)

1. Circuit arrangement for powering the analog functi on parts of several microcomputer-controlled analog dogital converters and analog value preprocessing modules from a common operating voltage source, characterized in that between the common operating voltage source ( 6 ) and the power supply inputs of the analog functional parts of the microcomputer-controlled analog-digital converter ( 31 , 32 , 3 n) and analog value preprocessing modules ( 21 , 22 , 2 n) each micro-computer-controlled all-pole disconnectors ( 41 , 42 , 4 n) are arranged and the power supply inputs of the analog functional parts of the analog-digital converter ( 31 , 32 , 3 n) and analog value preprocessing modules ( 21 , 22 , 2 n) associated auxiliary power sources ( 711 , 712 , 721 , 722 , 7 n1, 7 n2) are connected upstream, which supply power to the analog functional parts of the analog-digital converter ( 31 , 32 , 3 n) and analog value preprocessing modules ( 21 , 22 , 2 n) Open the all-pole disconnector ( 41 , 42 , 4 n). 2. Circuit arrangement according to claim 1, characterized in that electronic switches are used as microcomputer-controlled all-pole isolating switches ( 41 , 42 , 4 n). 3. A circuit arrangement according to claim 1 or 2, characterized in that energy storage components ( 711 , 712 , 721 , 722 , 7 n1, 7 n2) are used as auxiliary energy sources, each with a closed all-pole disconnector ( 41 , 42 , 4 n) absorb energy from the common operating voltage source ( 6 ). 4. A circuit arrangement according to claim 3, characterized in that capacitors ( 711 , 712 , 721 , 722 , 7 n1, 7 n2) are used as energy storage components, with one capacitor ( 711. ) At each pole of the operating voltage supply (+ U, -U) , 712 , 721 , 722 , 7 n1, 7 n2) is connected with one terminal and the other terminals of the capacitors ( 711 , 712 , 721 , 722 , 7 n1, 7 n2) are at the reference potential (AGND).