RU2507523C2 - Multi-channel device for measurement of insulation resistance in bundles and cables - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises N input precision resistors, the first analog-digital converter, to the middle point of power supply of which there is the first pole of a non-stabilised source of measurement DC voltage and a resistor, which is a current shunt, by the second output connected with the inlet of the first analog-digital converter, the outlet of which is connected to the inlet of a microprocessor element, connected with a source of measurement voltage, with a unit of digital indication of measurement results and modes of operation, with a unit of a keyboard, with an interface unit, an alarm unit and with control inlets of a switching unit. Also the device comprises the second analog-digital converter, inlets of which via a divider are connected with poles of a source of measurement voltage, and the outlet - with the inlet of the microprocessor element, and the switching unit comprises N switching units controlled with a microprocessor element, which comprise two switching elements, outlets of which are by the first contacts combined and connected to the second output of one of N input resistors, and the second contacts of the first switching element are connected with the second pole of the source of measurement voltage, and the second one - with the inlet of the first analog-digital converter.

EFFECT: possibility to measure resistance of insulation of each circuit, higher accuracy of measurements, possibility to control a metrological characteristic in process of operation.

2 dwg

Description

Multichannel device for measuring insulation resistance in bundles and cables.

The device relates to electrical engineering and is intended for use mainly in automated systems for monitoring, diagnostics and process control, and can also be used offline with the issuance of information on indicators.

Monitoring insulation and measuring its resistance for circuits galvanically isolated from the case (ground) have always been urgent tasks. The task of monitoring insulation between galvanically isolated circuits from the ground, especially between those passing in the same harness or cable, where there is a high probability of insulation failure between the circuits, leading to the possibility of electric shock to a person or disruption of the devices connected to these circuits, is also relevant.

A device for measuring insulation resistance (patent RU 2230332 G01R 27/16, published 10.06.2004), containing L input resistors, M measuring capacitors, several multiplexers and demultiplexers, a differential amplifier, an analog storage device, analog-to-digital Converter, control unit, indication unit, results calculation unit, etc., however, such a device has a very complex circuit, applicable for measuring the insulation resistance of only DC circuits, the principle of operation is based on measuring and non-linear processes of charge-discharge of capacitors (which cannot give high accuracy), the device is not applicable for measuring the insulation resistance between isolated circuits according to the principle of “each with each”.

A device for measuring electrical insulation resistance (patent RU 2348939 G01R 27/18, published March 10, 2009), designed for automated control systems in electric harnesses and cables, containing a test signal generation unit based on the DAC, a pump capacitor, a differential amplifier, analog a digital converter, a pump control unit, a time constant calculation unit, a measurement unit, etc., however, such a device also has a complex circuit, applicable for measuring insulation resistance only DC circuits, the principle of operation is based on the measurement of non-linear processes of charge-discharge of capacitors (which cannot give high accuracy), the device is not applicable for measuring the insulation resistance between isolated circuits according to the principle of “each with each”.

The closest analogue (prototype) of the proposed technical solution is an insulation resistance meter (patent for utility model RU 100631 G01R 27/16, published December 20, 2010) containing an input circuit, a control unit, a measurement unit, an analog-to-digital converter, a microprocessor unit, a unit digital indication of measurement results and operating modes, button keyboard unit, interface unit, alarm unit, multi-channel input circuit switching unit.

The disadvantages of the prototype are:

- the shaper of the measuring voltage to ensure the accuracy of the measurements must have strictly fixed parameters that vary in time according to certain laws (polarity reversal, multiple voltage changes), which complicates the device;

- the device is not applicable for measuring the insulation resistance between isolated circuits on the principle of "each with each."

The essence of the proposed technical solution lies in the fact that the known device containing N input precision resistors, the first conclusions of which form the inputs of the device, the first and second analog-to-digital converters, to the midpoint of the power supply of which is connected the first pole of the unstabilized source of measuring DC voltage and a resistor, being a current shunt, the second output is connected to the input of the first analog-to-digital converter, the output of which is connected to the input of the microprocessor element a, connected to a source of measuring voltage, with a digital display unit of the measurement results and operating modes, with a keypad block, with an interface unit, with an alarm unit and with the control inputs of the switching unit, while the inputs of the second analog-to-digital converter are connected via a divider with the poles of the measuring voltage source, and the output with the input of the microprocessor element, and the switching unit, in order to implement the measurement of the insulation resistance of each circuit both with respect to the "ground" and of other controlled circuits, as well as the implementation of the function of reversing the polarity of the leakage current of the voltage source of the controlled circuit flowing through the current shunt, contains N switching nodes controlled by a microprocessor element, comprising two switching elements, the outputs of which are connected by the first contacts and connected to the second output of one of N input resistors, and the second contacts of the first switching element are connected to the second pole of the measuring voltage source, and the second to the input at the same time, in order to control the metrological characteristics during operation, one of the switching nodes is designed to alternately turn on two accurate resistors between the second pole of the measuring voltage source and the input of the first analog-to-digital converter, characterized in that in order to reduce control inputs due to the use of the third output state of the microprocessor element switching nodes contain three transistors, emitters of which are connected to the common wire of the power source, the bases of the first and second transistors through limiting resistors are connected to the control input of the node, while the base of the first transistor is connected to the power bus through the resistor, and the second through the resistor to the common wire, the collector of the first transistor is connected to the base of the third and, through a resistor, with a power bus, and the switching elements are the collector loads of the second and third transistors.

The technical result is to simplify the switching unit by using the third state of the outputs of the microprocessor element.

Brief Description of the Drawings

Figure 1 shows the structural diagram of a multi-channel device for measuring insulation resistance in bundles and cables, where: 1 - the first analog-to-digital converter; 2 - midpoint power supply analog-to-digital Converter; 3 - source of measuring voltage; 4 - microprocessor element; 5 - block digital indication; 6 - block keypad; 7 - interface unit; 8 - alarm unit; 9 - the second analog-to-digital Converter; 10 - switching unit; 11 - switching nodes; 12 - switching elements; 13 - contacts of the switching elements; Ril-RiN - N input precision resistors; Rш - current shunt resistor; Rd1, Rd2 - voltage divider.

Figure 2 shows a diagram of a switching node, where: VT1-VT3 - the first, second and third transistors; R1-R5 - resistors; P1, P2 - the first and second switching elements.

The device shown in Figure 1 operates under the control of a microprocessor element (4) according to the program laid down in it. After turning on the power, in the initial state, the outputs of the microprocessor element that control the switching nodes (11) are in the third (high impedance) state and none of the input resistors (Ri1-RiN), the first output connected to one of the wires of the controlled circuits, is connected to the measuring inputs of the device, which are the input of the first analog-to-digital converter (1) and the second pole of the measuring voltage source (3). Before starting each measurement, the device monitors the metrological characteristics of the measuring channel by alternately connecting two built-in reference resistors (with ratings corresponding to the upper and lower parts of the measurement range) to the measuring inputs. At the same time, by issuing a "0" ("1") to the input of the corresponding switching unit, the microprocessor element connects the first (second) resistor and issues an enable signal to the converter of the measuring voltage source. Then he makes a time delay for the end of transients after turning on the source (3) and allows the ADC 1 and 9 to work, dividing the voltage according to the ADC 9 by the current according to the ADC 1 calculates the resistance values and turns off the source (3). If the measured values deviate from the calibration value stored in the memory, correction coefficients are calculated for further measurements, and if the established deviation norm is exceeded, it generates and transmits via the interface unit 7 to the automated system a sign of exceeding the measurement error in the oldest or youngest part of the measuring range or gives it to the display unit when working offline. Next, the process of measuring precisely the insulation resistance between successive circuits begins. Its difference is that the measurement is carried out in two stages: on the first microprocessor element, by issuing "O" to the first and "1" to the second switching nodes, it connects the monitored circuits to the measuring inputs, and in the second stage, it swaps them, issuing accordingly " 1 "and" 0 ". After that, the microprocessor element averages the voltage (ADC 9) and current (ADC 1) according to two stages (when summing the measurement results of two stages, the leakage current of the voltage source of the controlled circuit flowing through the current shunt is mutually subtracted), calculates the resistance of the entire circuit and subtracts from the result of the resistance value of the input resistors and the shunt resistor, thereby obtaining the value of the insulation resistance. The result, with a sign of compliance (non-compliance) with the norm for these circuits, is transmitted to the automated system or to the display unit, and with low resistance - to the alarm unit. The process is then repeated for other circuits.

If the device operates as part of an automated system, then at the upper level storage of configurations (maps) of measurements, as well as norms of limit values of insulation resistance for each circuit can be provided. The ability to work on certain configurations is provided in the microprocessor element program in order to shorten the overall measurement cycle, since there is no need to measure the insulation resistance between circuits located in different cables, but only within the group of circuits of one cable (bundle). In this case, the measurement relative to the "land" is always made.

The operation of the switching nodes 11 is illustrated by the diagram in Figure 2. To obtain the three states of the outputs of two switching elements ("both are turned off", "only the first is turned on", "only the second is turned on") using one output of the microprocessor element, two conditions must be met when calculating the circuit resistors :

U * R1 / (R1 + R3) <U _b

U * (R1 + R2 + R4) / (R1 + R2 + R3 + R4)> U _b ,

Where: U is the supply voltage, U _b is the unlock voltage of the base of transistor VT1.

In other words, the voltage of the dividers formed by the corresponding resistors at the point of connection to the base of the transistor VT1 (not) must exceed the voltage of unlocking the base.

Thus, with a logical zero at the input of the switching node, the first switching element is turned on, with - "1" - the second, and when the input is disabled (the output of the microprocessor element in the third state), both are turned off. Such a technical solution halves the required number of control outputs of the microprocessor element.

The present invention was used by Yugpromavtomatizatsiya NPP LLC in the development of IMSI modules, which are currently being put into trial operation as part of the automated system ADK-STsB at the Zeledeevo and Badalozhny railway stations of the Krasnoyarsk railway. The modules are certified as a measuring instrument as part of the IVK-TDM complex (Certificate of type approval of measuring instruments RU.C.34.004.A No. 36399).

Claims (1)

A multichannel device for measuring insulation resistance in bundles and cables of predominantly two-wire circuits, of any kind of current and de-energized, when connected to a single wire of a controlled circuit containing N input precision resistors, the first conclusions of which form the device inputs, the first analog-to-digital converter, to the midpoint the power of which is connected to the first pole of an unstabilized source of measuring DC voltage and a resistor, which is a current shunt, the second terminal is connected to the first analog-to-digital converter, the output of which is connected to the input of a microprocessor element connected to a measuring voltage source, with a digital display unit of the measurement results and operating modes, with a keypad unit, with an interface unit, with an alarm unit and with control inputs of the switching unit, at the same time, the inputs of the second analog-to-digital converter through a divider are connected to the poles of the measuring voltage source, and the output is connected to the input of the microprocessor element, and the unit Utility contains N controlled by a microprocessor element switching nodes, comprising two switching elements, the outputs of which are connected by the first contacts and connected to the second output of one of the N input resistors, and the second contacts of the first switching element are connected to the second pole of the measuring voltage source, and the second - with the input of the first analog-to-digital converter, while one of the switching nodes is designed to alternately turn on two accurate resistors between the second floor som of the measuring voltage source and the input of the first analog-to-digital converter, characterized in that the switching nodes contain three transistors each, the emitters of which are connected to the common wire of the power source, the bases of the first and second transistors are connected through the limiting resistors to the control input of the node, when the base of the first transistor is connected through the resistor to the power bus, and the second through the resistor to the common wire, the collector of the first transistor is connected to the base of the third and through the resistor with a power bus, and the switching elements are collector loads of the second and third transistors.

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