SU851415A1 - Pneumatic device for derivative sign determination - Google Patents

Description

(54) PNEUMATIC DEVICES FOR DETERMINATION The invention relates to instrument making and can be used in pneumatic controllers of variable structure for systems of automatic control of various technological processes. A pneumatic device for determining the sign of a derivative is known, containing a comparison element and a preliminary block and an adder connected to the input channel. The disadvantage of this device is low accuracy. It is also known a pneumatic device for determining the sign of the derivative containing a differential link connected to the input channel, output and negative feedback KciMepa connected to the input chambers of the first comparison element, the nozzles of which are connected to the input chambers of the second comparison element and through chokes - with the feed channel, each flow gauge of the first comparison element is connected through the choke with the atmosphere and directly with the corresponding nozzle of the three-membrane pb, le, -which communication MARK rotochnye DERIVATIVE chamber are connected with the atmosphere, a control input connected to the channel control signal, and an output of the second comparator connected to the output channel device r23. The disadvantage of this device lies in the complexity of its design. The purpose of the invention is to simplify the device. The goal is achieved by the fact that, in a pneumatic device containing a differentiating link connected to the input channel, the output and lagging negative feedback chamber of which are connected to the input chambers & -with the supply channel, both flow chambers of the first comparison element are connected; with the corresponding nozzles of the three-membrane relay, whose flow chambers are connected to the atmosphere, l yuschy input - channel control signal and the output of the second comparing element is connected to the output kangshu devices contained additional drosseb1 through which the first flow chambers comparing element are interconnected.

On the drawing e presents the scheme of the proposed device.

The device consists of three three-membrane elements 1-3 of comparison, pneumatic capacity 4, throttles 5 (adjustable), fixed chokes 6-8 and additional 9, as well as a three-voltage relay 10.

Comparison element 1, throttles 5 and 6, and air capacity 4 constitute the differentiating element. Positive cameras, reference 1 are connected to the input channel P. The minus chamber of element 1 (the output of the differentiating link) is connected to the first input chamber, element 1 and 2 of the comparison, directly through the nozzle with the atmosphere, through the throttle 6 through the power channel through the throttle 5 with pneumatic capacitance 4 by the second negative chamber of the element 1 zi) and the second input chamber of the comparison element 2 The nozzles of the element 2 are connected to the power channel through the throttles 7 and 8 and with the corresponding input chambers of the comparison element 3. The flow chambers of the comparison element 2 are connected to the corresponding nozzles of the three-membrane relay 10 and through daussel

9 between themselves. Flow chambers relays

10 communicated with the atmosphere. The pressure of the backwater is applied to one of the control chambers, and the control input is connected to the command signal channel 1. One nozzle of the comparison element 3 is connected to the atmosphere, the second is connected to the feed channel, and flow-through pumps with an outlet channel of the device.

The device works as follows.

In static mode (. 0)

d t

the input signals of the comparison element 2 are equal to each other and the output signal of the device определ is determined by the value of the signal P. At P 0, the nozzle in the upper (according to the drawing) flow chamber of the relay 10 is closed by the pressure of the overpressure and the nozzle in the lower one is open. The pressure in the lower flow chamber of element 2 is O, and in the other flow chamber of this same element, it is determined by the ratio of the conductivities of the drussels 7 and. Under the action of this pressure equal to 40-60 mm water column, the membrane unit of element 2 is shifted down, the pressure P after throttles 7 is less than the pressure P after throttles 8. As a result, due to unbalance at the inputs of element 3, the output signal of the device is equal to 1. At P 1, through the upper nozzle of the relay 10, the upper flow chamber of the element 2 is connected with the atmosphere, and in the other

the flow chamber of this element is set to a pressure of about 4060 mm water column, determined by the conductivity of the chokes 8 and 9. The diaphragm block of element 2 is 0.

neither shifted up, P,

g 7 Ra

and

bey

Over the course of dynamics (dP / dt 0), as a result of differentiating the input signal Pg, the input signals of the comparison element 2 become unbalanced. Since the effective areas affected by these signals are much (5-6 times) more efficient than the effective membranes of the flow chambers of this element, the position of the membrane unit is determined by the sign

5 of this imbalance. As the Ditch increases, the pressure in the lower entrance chamber of the element of comparison 2 is greater than at the upper, and regardless of the value of the command signal P, the membrane

0 unit element 2 is in the upper position, P 7 Pr and Pgjjjy, 0. When decreasing. the pressure in the lower inlet chamber of the reference element 2 becomes less than the pressure in the other

5 entrance chamber that provides

one.

and P,

R.PU

out

Thus, in dynamics, the value of the output signal of the device is determined by the direction of change of the input signal, and in statics, the value of the discrete command signal P,.

The technical and economic effect of the implementation of the proposed device is achieved by simplifying the design and tuning of the device, as well as by increasing the reliability of its operation.

Claims (2)

1. Berende TK, Efremova TK, Ta .gaevska A. A., h. Yuditsky S. A. Elements and pneumatic automation schemes M ,, Mashinostroenie, 1976, p. 140, fig. 1086. 2. USSR author's certificate 583445, cl. G 06 G 5/00, 1976 (prototype).   7 BUT