A System of Centralized Control, Monitoring, and Signaling

V. M. Novitskii, Yu. M. Ageev, M. S. Kadlubovich, V. N. Chudinov,
S. T. Yakovlev, A. I. Gering, A. K. Maier

(Presented by the scientific seminar of the Department of Automation and Telemechanics)

At the Department of Automation and Telemechanics of the Tomsk Polytechnic Institute, a system has been developed for centralized monitoring and signaling of the temperature regimes of electric furnaces, consisting of one dispatching station and twenty monitored points, each of which is intended to serve 20 objects (furnaces).

The system operates on the principle of cyclic polling of all monitored objects and is implemented mainly with contactless elements.

The polling cycle is carried out with a periodicity of once every 3 minutes, which corresponds to the requirements of the technological process. The polling speed without registration of information by the digital printing device is 10 points/sec. During registration—and the latter is performed only when the specified parameter (temperature) deviates by \(\pm 5^\circ\) from the established value and lasts 0.5 sec—the polling of objects is suspended.

The block diagram of the system is given in Fig. 1. The main units of the dispatching station, where registration and signaling of violations of the normal furnace regime are carried out, are: an electronic digital voltmeter of the EDV type; a digital printing machine of the TsPM-2 type; a commutator that sequentially connects all the commutated points to the dispatching station; a unit for signaling emergency regimes; and a command unit. The latter unit provides the issuance of advancing pulses at a frequency of 10 Hz and the issuance of synchronizing command pulses for starting the digital voltmeter. At each monitored point there is a group commutator, which provides the sequential connection of objects to the regulation and registration channel; a direct-current amplifier; a furnace temperature regulator; a device for compensating the temperature of the cold junctions of thermocouples; a temperature setter; and a local signaling unit.

The system is designed to maintain furnace temperatures in specified regimes within the range \(300^\circ\)—\(650^\circ\). Chromel—alumel thermocouples are used as temperature sensors; they can operate sufficiently reliably for a long time at temperatures up to \(900^\circ\).

Since the emf developed by a thermocouple depends on the temperature difference between its working junction, placed in the furnace, and the cold junction, which has the temperature of the surrounding medium, the system provides for thermostating of the cold junctions of the thermocouples by means of automatic compensation devices.

Fig. 1. Block diagram of the system

Visible labels in the diagram:

• DP
• Signaling unit
• Control unit
• Switch
• ZIV

• ChPM

• MP-1

• Signaling unit
• UPT
• Regulator
• Group switch
• Set-point unit
• Compensation device

• [[unclear: acronym in upper boxes, possibly “PSCh”]]

• MP-20

• Signaling unit
• UPT
• Regulator
• Group switch
• Set-point unit
• Compensation device

• [[unclear: acronym in upper boxes, possibly “PSCh”]]

• Channel markings: 1, 2, 20.

To set the required furnace temperature, a temperature setter is used, allowing the temperature to be set in the range of 300°–600° at intervals of 5°. When the furnace temperature deviates from the set value, a voltage equal to the difference between the thermo-e.m.f. and the voltage taken from the setter is fed to the DC amplifier (UPT) through the group commutator.

Taking into account that the input resistance of the DC amplifier is on the order of 1 kohm and that the total resistance of the measuring circuit does not exceed 50 ohms, the measurement error does not exceed 2.5°, i.e., 0.5%.

The sensors are connected to the DC amplifier and the individual actuating elements are simultaneously connected to the regulating device by means of a commutator made on small, high-speed RES-9 relays with two normally open contacts, which are energized in turn by the group distributor. The choice of a relay commutator is due to the requirement of minimal distortion of the weak signals coming from the sensors. The DC amplifier has an amplification factor of 500, zero drift of less than 20 μV, and sensitivity of 50 μV; its characteristic is linear for input signals from 0 to 2.52 mV.

The signal from the output of the UPT enters the regulation and signaling channels. The regulating device consists of a measuring converter (IP) and a phase-sensitive element (FChO). The measuring converter [2] is a device that produces rectangular pulses of stable frequency (5 kHz) and stable amplitude (5 V). The phase of these pulses depends on the polarity of the signal arriving from the DC amplifier. Since the sensitivity threshold of the converter is 40 mV, the regulator responds to a temperature deviation from the set value already at ±2.0°.

The phase-sensitive element, depending on the phase of the signal received from the measuring converter, produces a signal of one polarity or the other. When the furnace temperature exceeds the specified setpoint, the phase-sensitive element produces pulses of positive polarity; when the temperature decreases, pulses of negative polarity.

Control triggers are connected to the output of the phase-sensitive element through the contacts of the commutator; depending on the polarity of the pulses produced by the phase-sensitive element, they switch to one state or another. In this case, the control relays connected into the collector circuit of each trigger either switch on the contactor of the furnace heating element when its temperature decreases, or switch it off when the furnace temperature exceeds the setpoint.

The dispatcher station of the system uses mainly standard equipment—an electronic digital recording device, ETsR-1 (ETsV-1 electronic digital voltmeter, TsPP-2 digital printing machine, and KB-1 command unit), subjected to relatively minor modification.

Recording is carried out on paper tape; three digits are assigned to record the time of the temperature deviation (two digits for hours and one for tens of minutes), three digits to record the magnitude and sign of this deviation, two for the number of the furnace group, and two more for the number of the furnace in which the normal temperature regime has been violated.

The ETsV-3 electronic digital voltmeter, which is a multi-range high-speed voltmeter of high accuracy with a fully automated measurement process, receives signals from the DC amplifiers of the monitored points and converts—

converts them into binary code, issuing the information to a printing machine by means of the command unit.

Since the level of the signals arriving from the UPT is within the range \(0 \div 1.5\) V, for such a small range it is sufficient, without reducing measurement accuracy, to use only the two higher-order digits of the voltmeter. Because the digital machine must print not the voltage value but the temperature deviation, a diode decoder is installed between the electronic voltmeter and it, converting all values of the measured voltages into the corresponding temperature values. The sign of the temperature deviation comes directly from the digital voltmeter.

A furnace temperature deviation of \(\pm 40^\circ\) is an emergency condition, and in this case printing is carried out in red. Switching on the electromagnet of the coloring ribbon of the printing machine and the simultaneous switching on of the emergency alarm are performed by a signal from the ECV when a signal of \(\pm 0.8\) V arrives at its input, which corresponds to a temperature deviation of \(\pm 40^\circ\).

The two lower-order digits of the ECV are used as a counter of numbers within a group. This counter is built on two decades of a voltage-to-code converter (two open rings assembled on non-locking tyratrons of type TX4B) and is switched at a frequency of 10 cps by end-of-measurement pulses arriving from the voltmeter. The counter is reset by pulses arriving from each zero cell of each group distributor.

To convert the decimal code issued by the counter into the binary-decimal \((8, 4, 2, 1)\) code required for input to the printing machine, the corresponding code converters are used. A variant of autonomous implementation of the object-number counter without modification of the ECV is possible.

Counting of object group numbers is assigned to the input-channel counter of the command unit KB-1, assembled on non-locking tyratrons. Pulses to the input of this counter, and also to the control inputs of the electronic switches (the electronic commutator), arrive from the last cells of the group distributors and additionally, to improve operating reliability, from the object-number counter.

The decimal code issued by the counter goes to the corresponding converter for input to the CPM. Issuance of the time signal (hour and tens of minutes) at which a temperature deviation from the norm occurs is performed by the command unit. To start the printing machine and stop the scanning during registration, use is made of the fact that, when the temperature deviates from the specified norm that must be registered, a voltage exceeding \(0.1\) V appears at the voltmeter input.

In the developed system, several types of emergency signaling are provided: signaling of an emergency temperature runout, signaling of a sensor-circuit fault (break in the temperature circuit or shorting of the sensor to ground), signaling of a break in the heater spirals, and power-supply monitoring.

For signaling an emergency temperature runout, information from the digital voltmeter is used. When the sensor circuit is broken or it is shorted to ground, a signal from only the temperature setpoint device is applied to the DC amplifier. In this case the operating point of the amplifier shifts into the saturation region, and a voltage is taken from its output proportional to a temperature deviation of not less than \(60^\circ\), which is recorded by the digital voltmeter, acting on the corresponding emergency signaling.

Signaling of a break in the coils of the heating elements is based on a violation of load symmetry in the power circuit; monitoring of the power-supply units is carried out by means of the corresponding signal lamps on the dispatcher’s panel.

Since the ECR-1 device is designed for continuous operation for no more than 8 hours, while the centralized monitoring system must operate around the clock, it provides for two sets of ECRs with automatic switchover to reserve. This, together with the use of contactless equipment for almost all the other units and their block design, significantly increases the overall reliability of the system.

The system has undergone laboratory tests, which confirmed its high performance in terms of sensitivity, response speed, and reliability.

As a result, it should be noted that the developed system can be used for controlling production processes in the electrical-engineering, machine-building, chemical, and other industries, when the number of controlled objects reaches several hundred and the sensors produce comparatively weak signals.

REFERENCES

1. F. E. Temnikov, I. M. Shenbrot. Centralized Control Systems. Catalog-reference book, GOSINTI, 1964.

2. Yu. M. Ageev. Magnetic pulse-width DC converter. TPI, vol. 141, TSU Publishing House, 1966.