Control of chokes

Claim 2

A well choke control apparatus comprising: a. means for producing a first electrical signal indicative of a required position of the choke; b. means for deriving a second electrical signal indicative of the actual position of the choke; c. first comparator means, the first comparator means being arranged to be fed with said first and second electrical signals and to control actuation of the choke in the required direction to equalize said electrical signals; d. second comparator means; e. means settable to produce a third electrical signal indicative of a predetermined closed position of the choke; and f. override control means; the second electrical signal indicative of the actual position of the choke is also arranged to be fed as one input to the second comparator means, a further input of which is connected to the means settable to produce the third electrical signal, the output of the second comparator means being connected to said override control means which is arranged to prevent further actuation of the choke when said second and third signals are equal.

Claim 3

A well choke control apparatus as claimed in claim 1 further comprising: a. third comparator means; b. means settable to produce a fourth electrical signal indicative of a required predetermined open position of the choke; wherein the second electrical signal indicative of the actual position of the choke is also arranged to be fed as one input to said third comparator means, a further input of which is connected to said means settable to produce the fourth electrical signal, the output of the third comparator means being connected to said override control means arranged to prevent further actuation of the choke when said second and fourth signals are equal.

Claim 4

A well choke control apparatus as claimed in claim 2 further comprising: a. fourth comparator means; b. fifth comparator means; c. means arranged to produce a fifth electrical signal representative of a substantially closed position of the choke; e. means arranged to produce a sixth electrical signal representative of a substantially open position of the choke, and e. second override means, wherein the second electrical signal indicative of the actual position of the choke is also arranged to be fed as one input of both said fourth and fifth comparator means, a second input of the fourth comparator means is connected to said means arranged to produce the fifth electrical signal, a second input of the fifth comparator means is connected to said means arranged to produce the sixth electrical signal and the outputs of both fourth and fifth comparator means being connected to said second override means arranged to disconnect power from the control apparatus when the inputs to respective fourth or fifth comparators are equal.

Claim 5

A well choke control apparatus comprising: a. means for producing a first electrical signal indicative of a required position of the choke; b. means for deriving a second electrical signal indicative of the actual position of the choke; and c. first comparator means, said first comparator means comprising two pairs of buffer amplifiers, the first and second signals being fed as inputs to respective first and second buffer amplifiers of each pair, and three differential amplifiers, the first differential amplifier deriving inputs from one pair of buffer amplifiers and having its output connected to control means to control actuation of the choke in one direction, the second differential amplifier deriving inputs from the other pair of buffer amplifiers and having its output connected to further control means to control actuation of the choke in the other direction, and the third differential amplifier deriving inputs respectively from the first buffer amplifier of one pair and the second buffer amplifier of the other pair and having its output connected to third override control means capable of overriding control from the control means and further control means.

Claim 6

A well choke control apparatus comprising: a. means for producing a first electrical signal indicative of a required position of the choke; b. means for deriving a second electrical signal indicative of the actual position of the choke; and c. first comparator means, said first comparator means comprising two pairs of buffer amplifiers, the first and second signals being fed as inputs to respective first and second buffer amplifiers of each pair, and three differential amplifiers, the first differential amplifier deriving inputs from one pair of buffer amplifiers and having its output connected to control means to control actuation of the choke in one direction, the second differential amplifier deriving inputs from the other pair of buffer amplifiers and having its output connected to further control means to control actuation of the choke in the other direction, and the third differential amplifier deriving inputs respectively from the first buffer amplifier of one pair and the second buffer amplifier of the other pair and having its output connected to third override control means capable of overriding control from the control means and further control means.

Claim 7

A well choke control apparatus as claimed in claim 4, wherein the control means and further control means are connected to means arranged to control a timing circuit which produces timed output pulses for connection to actuation means for the choke.

Claim 8

A well choke control apparatus as claimed in claim 5 wherein said control means, further control means and said further override control means comprise electromagnetic relays.

Claim 9

A well choke control apparatus as claimed in claim 4 including means for operating the apparatus from a remote location by disconnecting the means for producing said first electrical signal and substituting remotely produced control pulses therefor.

Claim 10

A well choke control apparatus comprising: a. means for producing a first electrical signal indicative of a required position of the choke; b. means for deriving a second electrical signal indicative of the actual position of the choke, the means for producing the first and second signals comprising a resistive bridge including terminals which, in use, are connected to a potentiometer located on the choke and arranged to be actuated with actuation of the choke; c. means for calibrating said means for producing the first and second signals; and d. first comparator means, the first comparator means being arranged to be fed with said first and second electrical signals and to control actuation of the choke in the required direction to equalize said electrical signals.

Claim 11

A well choke control apparatus comprising: a. means for producing a first electrical signal indicative of a required position of the choke; b. means for deriving a second electrical signal indicative of the actual position of the choke, the means for producing the first and second signals comprising a resistive bridge including terminals which, in use, are connected to a potentiometer located on the choke and arranged to be actuated with actuation of the choke; c. means for calibrating said means for producing the first and second signals; and d. first comparator means, the first comparator means being arranged to be fed with said first and second electrical signals and to control actuation of the choke in the required direction to equalize said electrical signals.