Two wire command and monitoring system

An improved system and method for transmitting and monitoring, for example, commands to relays or other output command devices driving controlled devices remotely located from the transmission portion of the transmission and monitoring system. The system is usually divided into two parts geographically separated by a significant distance with two wires running between the parts. The first part is used for transmitting the command and interrogation signals through the use of current levels set by overall circuit characteristics and produced on alternate positive and negative half cycles by an alternating current source and set by the resistive load in the loop. The second part is for interpreting the signal by relay discrimination to determine if it is a command or just the interrogation signal requesting the current state of the device being controlled by the system and also for local indication. During operation, when no commands are being sent to the receiving part, the signals indicate the present state of remote contacts that represent the positional state of the controlled device. When a command is to be sent to the receiving part, the current is changed by resistive load change to a new level which represents the command to be transmitted to the receiving part. The improvement prevents the stop command from actuating the system in an improved manner rather than stopping the controlled device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved data transmission and 
monitoring system and method for transmitting and monitoring commands to 
devices including commands to open or close a valve or stop the valve 
somewhere in the middle of its travel. The present invention has been 
found to be particularly useful in the discrete state command and 
monitoring transmission art in industrial environments, especially as a 
device for controlling and monitoring motors and valves, and, hence, will 
be discussed with particular reference thereto. However, the present 
invention is applicable to many other types of discrete commands as well, 
as long as each operation on the device is of a discrete nature as opposed 
to continuous nature. 
2. Description of the Prior Art 
In the transmission and detection of commands to valves and motors, 
transmission systems are usually divided into two portions, one located 
where the commands are to originate, either by an automatic system or by a 
manual request from a human operator, and the other where the command is 
detected and routed to activate the controlled device and indicate the 
present state of the controlled device locally, as well as transmit the 
state back to the transmission means. Additional components are used to 
transmit the signal from the transmission portion to the receiving 
portion, including a power source to activate both the transmission and 
the receiving portion simultaneously and wires for carrying the signal. 
The system must be capable of transmitting signals to the remote location 
in such a manner that environmental factors which usually exist in 
industrial plants will not affect the signals transmitted. The system must 
also be reliable in operation for a long period of time and consistent in 
its manner of operation. In addition, the system must correctly perform a 
stop function to prevent actuation of the device. 
Several types of transmission and detection systems have been known and 
used before, and typical examples thereof in the valve and motor command 
monitoring art are shown in U.S. Pat. No. 3,256,517, issued June 14, 1966, 
to T. Saltzberg et al.; U.S. Pat. No. 3,289,166, issued Nov. 29, 1966, to 
D. G. Emmel; U.S. Pat. No. 2,360,172, issued Oct. 10, 1944, to C. E. 
Stewart; U.S. Pat. No. 2,788,517, issued Apr. 9, 1957, to W. L. Smoot et 
al.; U.S. Pat. No. 3,251,992, issued May 17, 1966, to R. B. Haner, Jr.; 
U.S. Pat. No. 3,315,231, issued Apr. 18, 1968, to P. Belugou; U.S. Pat. 
No. 3,254,335, issued May 31, 1966, to R. J. Staten; U.S. Pat. No. 
3,202,978, issued Aug. 24, 1965, to G. E. Lewis; U.S. Pat. No. 2,525,016, 
issued Oct. 10, 1950, to G. L. Borell; U.S. Pat. No. 2,003,047, issued May 
28, 1935, to S. C. Henton et al.; U.S. Pat. No. 2,019,350, issued Oct. 29, 
1935, to R. Koberich; U.S. Pat. No. 2,260,061, issued Oct. 21, 1941, to C. 
E. Stewart; U.S. Pat. No. 2,992,366, issued July 11, 1961, to T. E. 
Veltfort, Jr.; U.S. Pat. No. 3,185,911, issued May 25, 1965, to H. Epstein 
et al.; U.S. Pat. No. 3,629,608, issued Dec. 21, 1971, to Joseph W. 
Trindle; and U.S. Pat. No. 3,398,329, issued Aug. 20, 1968, to J. B. 
Cataldo et al. 
The Saltzberg, Emmel and Stewart data transmission and collection systems 
use conventional coding techniques such as pulse coding or tone 
transmission to transmit information from the transmission device to the 
receiving device. However, this type of prior art requires complex logic 
for encoding and decoding data at the transmission device and at the 
receiving devices. 
The Smoot, Haner, Belugou, Staten, Lewis, Trindle, Epstein and Borell 
devices use either direct current signals to transmit the information or 
three wires to transmit the information from the transmission device to 
the receiving device, requiring relatively high sustained voltage values 
which would be unsafe in an industrial environment or additional stringing 
of wires over long distances. 
The Henton, Koberich, Stewart and Veltfort devices all use a different 
polarity current in a two-wire mode to transmit information from the 
transmission device to the receiving device but none of them disclose a 
stop function. 
Another alternating polarity current transmission system is disclosed in 
FIG. 1 which has been used publicly and is part of the prior art. This 
system, however, requires additional relay contacts, as will be discussed 
in the Detailed Description of the Preferred Embodiment, to prevent the 
stop function from actuating the controlled device to move rather than to 
stop the controlled device. 
SUMMARY OF THE INVENTION 
The present invention uses a very simple but highly effective means to 
electrically prevent signals from being transmitted to a controlled device 
when a stop request is made. This means interlocks the stop request 
function with the known state of the controlled device and prevents 
initiation of the stop request if the controlled device has already 
stopped in an extreme position reflected by the circuit feedback contacts 
from the controlled device without the use of additional relay contacts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Introduction 
The improved data transmission and monitoring system of the preferred 
embodiment may be used for control and monitoring of discrete actuation 
controlled devices connected to the system such as valves or motors 
wherein it is important that the devices controlled and monitored be 
remotely located from the transmission portion of the system with 
prevention of erroneous actuation of the controlled device by use of a 
stop function. A particularly important application of the present 
invention is in the control and monitor of valves in industrial plants 
using open and close commands, as well as a stop command for stopping the 
valve during its travel from the open to the closed state, and, therefore, 
the preferred embodiment will be described with respect to such an 
application. However, it should be realized that the present invention 
could be applied to, for example, any application where it is desired to 
transmit discrete information from one location to another using variable 
current levels in the form of commands to controlled devices and monitor 
the results of those commands wherein the state of the controlled device 
and a command must be interlocked. 
In the preferred embodiment of the present invention, the transmission is 
accomplished through the use of two circuit resistance set levels of 
current on each half cycle of an alternating current power supply for 
monitoring the state of the controlled device and for open/close valve 
commands. These commands are electrically isolated from the circuitry that 
actuates the device by relay isolation. The current level of the signals 
is determined by the circuit resistance, a characteristic of the relays, 
lines, and other resistance used in the circuit. This resistance is varied 
when a command to the controlled device is initiated by some circuit 
resistance being changed thereby raising current level on one of the half 
cycles of the alternating current power supply. The commands are decoded 
by current level using relay detection. A stop function is implemented to 
terminate activation of the valve before it has reached the extreme 
position of its travel. This stop function is accomplished through 
interlocks in the relay actuation circuitry of the controlled device. The 
transmission portion of the system actuates the stop function by imposing 
raised current levels on consecutive half cycles at the alternating 
current power supply. The improved circuit prevents the stop function 
initiation when the valve is in either extreme position of travel as 
indicated by discrete state feedback. 
Structure and Operation 
Referring to FIGS. 1 and 3, there are shown data transmission and 
monitoring systems as two-part systems. The transmission and indication 
parts 1,1' of the systems respectively of FIGS. 1 and 3 are composed of 
current driving means comprising relays 7 and 10 wired in series with 
power supply 33. The current through each relay 7, 10 is determined by the 
circuit resistance for the appropriate polarity of power supply 33 when 
current is conducting through the relay, including the resistance of the 
relays 7, 10. Diodes 11 and 12 respectively in series with the relays 7, 
10 protect them and prevent their conduction to actuation levels during 
the inappropriate circuit polarity of power supply 33. Wired in parallel 
with the relays 7 and 10 are push button actuated switches 3 and 4 
respectively labelled OPEN and CLOSE. Relays 7 and 10 have associated 
contacts 17 and 27 respectively. Contacts 17 and 27 are wired in series 
with lights 21 and 24 respectively labelled OPEN and CLOSE. The contacts 
17 and 27 and lights 21 and 24 are connected to power supply 22. It is 
also well known in the art to remotely control lights 21 and 24 by the use 
of the contacts, additional relays or other means if it is desired to 
remotely locate them. Each relay 7, 10 has associated with it a capacitor 
28, 30 respectively to prevent surges and noise actuation of the system. 
These capacitors also keep the relays 7 and 10 energized for the alternate 
half cycle of power supply 33. 
In FIG. 1, the transmission and indication part 1 also has relay contacts 
6, 8 associated with relays 7, 10 respectively. Contacts 6, 8 are 
connected in series to each other and in series with capacitor 13 and push 
button actuated switch 5 labelled STOP, all being in parallel with both 
relays 7 and 10. 
In FIG. 3, the transmission and indication part 1' has capacitor 16 
connected in series with push button actuated switch 5 labelled STOP, both 
being in series with power supply 33 and transmission line 1000. 
The transmission and indication portions 1,1' of the systems of FIGS. 1 and 
3 respectively are connected to conductors 320 and 1000. Also connected to 
the conductor 320 is power supply 33. Conductors 320 and 1000 are 
connected between monitoring and control part 2 of the systems and 
transmission and indication portions 1,1' of the systems. 
The monitoring and control part 2 of the systems comprises current level 
actuation means, relays 43 and 54. Capacitors 42 and 44 are wired in 
parallel to relays 43 and 54 respectively to prevent surges and noise 
actuation of the systems. These capacitors also keep the relays 42 and 44 
energized for the alternate half cycles of power supply 33 above the 
appropriate current level. Diodes 46, 47 respectively in series with 
relays 43 and 54 protect and prevent the relays 43 and 54 from passing 
current during the inappropriate circuit polarity of power supply 33. When 
the level of current passing through the relay 43 or 54 reaches a value 
sufficient to energize the relays, relay 43 or 54 will close its contacts 
93 or 94 respectively which will energize coil 950 or coil 960 (FIG. 2). 
As best shown in FIG. 2, contacts 93 connected at 101 and 94 connected at 
107 of relays 43 and 54 respectively and contacts 96b and 95a of the 
controlled device indicating, the extreme states of the controlled device, 
are connected in series with each other respectively and in series with 
fuse 91, effective relay contact 92, relay contacts 97 of overload 
sensors, time delay relay contact 103, and relay coils 950 and 960, all 
between the high side 90 of a power supply and the neutral 98. Relay coils 
950 and 960 have contacts 95 and 96 respectively wired in parallel with 
contacts 93 and 94 respectively to lock in contacts 93 and 94 for 
continued activation of the controlled device after the relay 43 or 54 no 
longer has sufficient current to stay actuated. Effective relay contact 92 
is made up in part of contacts 92' and 92" respectively of relay 43 and 54 
wired in parallel. It also has a time delay relay contact 103 in series 
with contacts 92' and 92". 
Relay coils 950 and 960 are connected to the controlled device by contacts 
not shown and the state of the controlled device is given by contacts 45 
and 56 (FIGS. 1 and 3) wired in series with relays 54 and 43 respectively. 
In the preferred embodiment for illustration purposes, it should be 
recognized that contacts 45 and/or 56 are closed when the controlled 
device is not in the state represented by the contact. Therefore, both 
contacts 45 and 56 will be closed while the controlled device is in 
transit. The controlled device will open either contact 45 or 56 upon 
reaching the end position represented by contact 45 or 56 respectively. If 
the controlled device (valve) is in the "open" position, it will force 
contact 45 open. If the controlled device (valve) is in the "closed" 
position, it will force contact 56 open. The opening of these contacts may 
be by either mechanical, electrical, or electronic linkage. 
As shown in FIG. 1 or FIG. 3, neither "open" pushbutton actuated switch 3 
nor "close" pushbutton actuated switch 4 is in an actuated, depressed 
state. 
Under these conditions, if the system were in a quiescent state with the 
controlled device either in one or the other of its terminal positions, 
closed or opened, either "open" contact 45 or "close" contact 56 would be 
closed and the other would be open. 
For purposes of illustration only, presume that "close" relay contact 56 
were closed and "open" relay contact 45 were open, indicating that the 
controlled device is in the open position. During every positive 
half-cycle of the power supply 33, this would cause current to flow 
through relay 7. Obviously, diode 12 would prevent any actuation of relay 
10 during the positive half-cycle of the power supply 33, as does diode 11 
prevent any actuation of relay 7 during the negative half-cycle of the 
power supply 33. 
During the positive half-cycle of power supply 33, the current has only one 
path to go from relay 7. It will flow through conductors 320, 1000 to the 
"close" contact 56 which is closed because the controlled device is not in 
the closed state. 
Relays 7 and 10 are selected to have a resistive characteristic so that 
insufficient current is generated to actuate relays 43 and 54 respectively 
but to permit actuation of relays 7 and 10. Therefore, all current 
generated through conductor 320 will flow through contact 56, through 
relay 43 without actuating the relay, through diode 46, through relay 7, 
and through diode 11, returning to power supply 33. Therefore, current not 
being sufficient to actuate relay 43, the system will stay in a quiescent 
state with light 21 lit through closure of contact 17 by relay 7. 
Capacitor 28 will keep the relay 7 actuated during the negative half-cycle 
of power supply 33. This will indicate, without control action being 
taken, that the present state of the controlled device is, for example, 
open. The source of power for light 21 is voltage supply 22 conducting 
through contact 17 to light 21. 
During the negative half-cycle of the power supply 33, no conduction will 
take place. Contact 45 is open, as a result of the controlled device 
indicating that it is already in the open state through contact 45 
opening, and, therefore, there is no path for current to flow. 
When the "close" pushbutton is depressed actuating closed pushbutton 
actuated switch 4, a different level of current will be allowed to flow 
through relay 43 from the power supply 33 on each positive half-cycle 
because relay 7 and capacitor 28 are shorted by the closure of pushbutton 
actuated switch 4. This current will exceed the current level necessary to 
actuate relay 43. 
With relay 43 actuated, relay contact 94 will be closed and relay contact 
92' will be opened. Relay contact 92" will still be closed so that the 
effective relay contact 92 of FIG. 2 will remain in a closed state. As 
best seen in FIG. 2, the closure of contact 94 will cause the actuation of 
control device coil 960 of relay M-2, by the current path from the voltage 
source 90, to fuse 91, through time delay relay contact 103 and closed 
contact 92 and closed contact 94 to coil 960 of relay M-2, through 
overload closed contact(s) 97 to neutral 98. Capacitor 42 will keep relay 
43 actuated during the negative half-cycle of power supply 33. This will 
cause the control device to go to its other state. 
While the control device such as, for example, a valve is in transit, both 
contacts 45 and 56 would be closed by techniques well known in the art, 
and current is permitted to flow during both half-cycles of power supply 
33. The levels of current on each half-cycle of power supply 33 will not 
be the same so long as pushbutton actuated switch 4 is depressed and 
pushbutton actuated switch 3 is not depressed. 
Of course, the current path during the negative half-cycle of power supply 
33 through conductors 320 would be identical in method of actuation to the 
path during the positive half-cycle when pushbutton 4 is not depressed. 
Therefore, current during the negative cycle would flow through diode 12, 
through relay 10, through conductors 320 and 1000, through diode 47, 
through relay 54, through contact 45, and to power supply 33. Relay 10 
would also close contact 27 which would cause light 24 to go on. 
After pushbutton actuated switch 4 is released, light 21 would also go on 
again. It, of course, would have been off while relay 7 was shorted 
because contact 17 would have been open. Therefore, while the control 
device is in transit, and after the pushbutton 4 has been released, 
transmission portion 1 or 1' would indicate to the operator that both 
contacts 45 and 56 were closed by lights 21 and 24 being lit. 
When the controlled device (valve) has completed its travel to the opposite 
or closed state, then contact 56 would be opened by methods well known in 
the art thereby preventing any current flow during the positive half-cycle 
of the power supply 33. Contact 95a would also be opened by the controlled 
device by methods well known in the art thereby stopping the current to 
motor relay coil M-1, 950. The only current path remaining would be that 
corresponding to relay 10 conducting to relay 54. Therefore, light 24 at 
the transmission portion 1 or 1' would stay lit while light 21 would be 
extinguished. Relay 54 would not be actuated until the "open" pushbutton 
actuated switch 3 is depressed because of the resistance characteristics 
of relay 10 keeping the current level below the actuation level of relay 
54. 
Therefore, there are four discrete current levels available in the system 
of either the prior art or the present invention, two during the positive 
half-cycle of power supply 33 and two during the negative half-cycle of 
power supply 33. These currents are all set by the resistance 
characteristics of the relays, lines, and other circuit resistances. One 
level of current in either the positive half-cycle for relay 7 or negative 
half-cycle for relay 10 of power supply 33 is produced when no pushbutton 
is depressed. The other level of current in either the positive or 
negative half-cycle, respectively, would occur as a result of shorting 
relay 7 or 10. These latter currents are imposed as a result of closures 
of either the "open" or "close" pushbuttons, while corresponding field 
contact 56 or 45 is closed. 
It should be noted that, with proper relay configuration, the depression 
simultaneously of the "open" and "close" pushbuttons 3 and 4 during the 
transit of the controlled device (valve) between its open and its close 
position could stop the controlled device (valve) by interrupting the 
current to drive relay coils M-1 and M-2. This is accomplished in the 
circuits of FIGS. 1 or 3 by the use of pushbutton actuated switch 5 
labelled STOP which has the effect of the simultaneous depression of 
pushbutton actuated switches 3 and 4. When pushbutton actuated switch 5 is 
depressed, both relays 7 and 10 are shunted on alternate half-cycles by 
capacitor 13 and actuation current levels are impressed on lines 320 and 
1000 on alternate half-cycles. Therefore, both contacts 92' and 92" will 
be opened simultaneously as contacts 93 and 94 are thereby closed which 
effectively opens contact 92, being in part the representation of contacts 
92' and 92" wired in parallel. This will cause a momentary break in the 
circuit which will cause interruption of the current to relay coils 950 
and 960 of relays M-1 and M-2 causing contacts 95 and 96 to drop out and 
no longer latch-in the actuation of coils 950 and 960 of relays M-1 and 
M-2. This would stop the controlled device (valve) somewhere intermediate 
in travel of the controlled device (valve) to either end state. By again 
depressing either the "open" pushbutton actuated switch 3 or "close" 
pushbutton actuated switch 4, travel of the controlled device (valve) can 
again be started because contacts 45 and 56 are both still closed. 
Therefore, upon actuation of either pushbutton actuated switch 3 or 
pushbutton actuated switch 4, either relay 43 or relay 54 will again 
energize, i.e. so long as only one pushbutton, either "open" or "close" is 
depressed, then the opposite contact, either contact 92" or contact 92', 
respectively, will be closed permitting current to flow from power source 
90 to neutral 98 through effective contact 92. 
With the circuit as shown in FIG. 1 or 3, the depression of pushbutton 
actuated switch 5 would, however, still not be sufficient to prevent the 
occasional restarting of the controlled device (valve) as a result of a 
race after stopping action. As just discussed, the controlled device 
(valve) can be stopped in midtravel by the opening of both normally closed 
contacts 92' and 92". When pushbutton 5 is released however, relay 43 may 
de-energize before 54 does or vice versa, thus creating a condition in 
FIG. 2 where contact 92" is closed and contact 94, the normally open 
contact of relay 43, is still closed thus energizing relay 960. Relay 960 
then seals in through its contact 96 thus remaining energized until 
contact 96b opens at the end of travel. It is well known, however, in the 
art to use a time delay relay or other means to activate time delay relay 
contact 103 in series with effective relay 92 to prevent this relay "race" 
by holding the contact 103 open until all other contacts have settled. 
There is a disadvantage to using pushbutton actuated switch 5 with the 
prior art circut shown in FIG. 1. Without additional relay contacts 6, 8 
of FIG. 1, the depression of pushbutton actuated switch 5 when the 
controlled device (valve) is in either the fully open or fully closed 
position, as reflected by contact 45 or contact 56 being closed, would 
cause the controlled device (valve) to start moving to the other position. 
If contact 45 is open, only relay 43 will energize, even if pushbutton 
actuated switch 5 is depressed, because there is no conduction during the 
negative half-cycle of power supply 33. The depression of the "stop" 
pushbutton therefore would be equivalent to the "close" pushbutton being 
depressed which is opposite the desired function of the "stop" pushbutton. 
As shown in FIG. 1, additional contacts 6, 8 are used in the prior art to 
eliminate unwanted actuation when the "stop" pushbutton is depressed with 
the controlled device (valve) being in either extreme of its travel. As 
shown in FIG. 1, the "stop" pushbutton 5 would not be effective unless the 
valve or other control device were in transit. When the control device is 
in transit, both relays 7 and 10 would be energized on alternate 
half-cycles of power supply 33 and kept actuated on the other half-cycle 
by capacitors 28, 30 respectively because both contact 45 and contact 56 
are closed. The interlocking of pushbutton actuated switch 5 with 
conduction in alternate half-cycles of power supply 33 is accomplished by 
placing relay contacts 6 and 8 of relays 7 and 10 in series with power 
supply 33 to pushbutton 5. Capacitor 13 in combination with capacitors 28, 
30 is used to prevent contacts 6, 8 from "chattering" i.e. prevents 
bouncing of the contacts on actuation. This prior art method of 
interlocking, however, requires the use of the additional relay contacts 
6, 8 for each relay 7, 10 respectively which is expensive. 
The apparatus of the preferred embodiment of the present invention of FIG. 
3 uses capacitor 16 which is properly sized to quickly charge, prior to 
the reaction time at relays 43, 54, to the peak value of power supply 33 
for successive half-cycles of the same polarity from power supply 33 for 
either the positive or negative half-cycle of power supply 33 if such 
half-cycle is not followed by the next sequential half-cycle of opposite 
polarity. Additionally, resistor 5', such as 10,000 ohms, is connected in 
parallel with switch 5. In this manner, when the controlled device is not 
in transit, then resistor 5' will permit capacitor 16 to bleed charge to 
the voltage level of power supply 33 over the number of cycles determined 
by the product of the capacitance of capacitor 16 and resistance of 
resistor 5'. The value of the resistor is set high to keep the bleed 
charge current well below any actuation levels for relays 43, 54. Of 
course, if the controlled device is in transit, the conduction through 
capacitor 16 and resistor 5' on both half cycles will prevent such a 
build-up. Therefore, the slow charge of capacitor 16 when the controlled 
device is not in transit prevents the necessity of charging up the 
capacitor upon depression of pushbutton 5. Therefore, there is no 
beginning current because of the charging pulse to capacitor 16 upon 
depression of pushbutton 5, eliminating any possiblity of triggering 
relays 43, 54 if they should be sensitive. In this manner, the need for 
additional contacts for relays 7, 10 is eliminated because capacitor 16 
will charge and therefore effectively open the part of the circuit where 
pushbutton actuated switch 5 is located, before pushbutton actuated switch 
5 is closed when the valve or other controlled device is not in transit, 
by presenting an equal and opposite voltage to the voltage level of power 
supply 33. 
Although the system as described in detail supra has been found to be most 
satisfactory and preferred, different applications and many variations in 
its elements and the structure of its elements are possible. For example, 
the system of the present invention can be used to faciliate motor start 
and stopping. Moreover, the system of the present invention can be 
equipped with fault detection means that would respond to no current 
flowing in successive half-cycles of power supply 33 to indicate equipment 
failure. Additionally, triac or other output devices may be substituted 
for output relays. Also, additional means may be employed to transmit the 
actual position of the valve or other control device to the transmission 
portion of the syste to permit precise control of the position of the 
valve through remote actuation means. Moreover, two control devices may be 
controlled and monitored if they have only a single state through one 
system. Also, instead of lights in the transmission and indication portion 
of the system, relays could be used in the transmission and indication 
portion of the system that would actuate lights and other devices. Also 
the relays could be actuated by means remote from the transmission and 
indication means rather than pushbuttons. 
The above are merely exemplary of the possible changes or variations. 
Because many varying and different embodiments may be made within the scope 
of the inventive concept herein taught, and because many modifications may 
be made in the embodiment herein detailed in accordance with the 
descriptive requirements of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not in a limiting 
sense.