Position transmitter for a pneumatic-pneumatic or electro-pneumatic converter

• US 4,731,996 A
• Filed: 09/10/1984
• Issued: 03/22/1988
• Est. Priority Date: 09/10/1984
• Status: Expired due to Fees

• Current Assignee: Elsag International BV (ABB Limited)
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Smith, Jane E., Sampson, Raymond J.
• Primary Examiner(s): Look, Edward K.
• Application Number:
  US06/649,246
• Time in Patent Office: 1,289 Days
• Field of Search: 318/663, 60/388, 60/390, 60/391
• US Class Current: 60/390
• CPC Class Codes: G05D 3/1472 with potentiometer

Abstract

A position transmitter which can be incorporated in a pneumatic-pneumatic or electro-pneumatic converter, and which readily provides for calibration between a zero position and a maximum position of a device to be actuated by the converter. The invention also provides a virtually non-interacting zero and span or full scale adjustment, for ease of calibration.

Claims

1. A position transmitter for generating a signal corresponding to the position of a movable member of an actuator device, comprising:

a DC power supply having a pair of terminals;

an input line connected to one terminal of said power supply;

an output line connected to the other terminal of said power supply;

voltage divider means connected between said input and output lines and having a movable contact mechanically engageable with the movable member of the actuator device for carrying a voltage which varies with motion of the movable member;

a zero adjust amplifier having an input connected to said movable contact for receiving the voltage carried by said movable contact, and an output, said zero adjust amplifier being connected to influence a current on said output line and having an adjustable input, said movable contact being movable to a zero position corresponding to a zero position of the movable member and said adjustable input being adjusted to apply a low selected current signal to said output line which is indicative of a zero position of the movable member;

a span adjust amplifier having an input connected to said output of said zero adjust amplifier, said span adjust amplifier having an output and being connected to influence a current on said output line, said span adjust amplifier having an adjustable input, said movable contact being movable to a maximum position corresponding to a maximum position of the movable member and said adjustable input of said span adjust amplifier being adjusted to apply a high selected current signal to said output line which is indicative of the maximum position of the movable member; and

a voltage-to-current stage connected between said input and output lines and connected to said output of said span adjust amplifier for converting a voltage signal from said span adjust amplifier to a current signal on said output line.

2. A position transmitter according to claim 1, wherein said voltage divider means comprises a potentiometer resistor connected across said input and output lines, said movable contact comprising a wiper engage with said potentiometer resistor, a first resistor connected in said input line and a second resistor connected in said output line.

3. A position transmitter according to claim 2, wherein said DC power supply has a positive terminal connected to said input line and a negative terminal connected to said output line, a first amplifier having a positive input connected to said wiper and an output, said zero adjust amplifier having a negative input connected to said output of said first amplifier, a second potentiometer resistor connected across said input and output lines, a second wiper engaged with said second potentiometer resistor and connected to a positive input of said zero adjust amplifier, said span adjust amplifier having a negative input connected to said output of said zero adjust amplifier and having a negative feeback line having a third potentiometer resistor therein, a third wiper engaged with said third potentiometer resistor and connected to said negative feedback line whereby said zero adjust amplifier has an adjustble input comprising said second potentiometer resistor and wiper and said span adjust amplifier has an adjustable input comprising said third potentiometer resistor and wiper.

4. A position transmitter according to claim 3, wherein said voltage-to-current converter comprises a transistor having an emitter and collector connected across said input and output lines, and a base, a further amplifier having a negative input connected to said output of said span adjust amplifier, and an output connected to said base for controlling the conductivity of said transistor to apply a variable current to said output line with variations in voltage from said span adjust amplifier.

5. A position transmitter according to claim 4, including a first diode connected between said positive terminal of said DC power supply and said input line for conducting current toward said input line and a second diode connected between said output line and said negative terminal of said DC power supply for conducting current toward said negative terminal, and a third diode connected between said transistor and said output line for conducting current from the transistor to the output line, said first, second and third diodes provided for protecting against reverse current in said input and output lines.

6. A position transmitter according to claim 5, including a Zener diode connected between said input and output lines adjacent said first and second resistors for limiting a voltage across said input and output lines.

7. A combination of a position transmitter and a system controller comprising:

a DC power supply having a pair of terminals;

an input line connected to one terminal of said power supply;

an output line connected to the other terminal of said power supply;

voltage divider means connected between said input and output lines and having a movable contact mechanically engageable with the movable member of the actuator device for carrying a voltage which varies with motion of the movable member;

a zero adjust amplifier having an input connected to said movable contact for receiving the voltage carried by said movable contact, and an output, said zero adjust amplifier being connected to influence a current on said output line having an adjustable input, said movable contact being movable to a zero position corresponding to a zero position of the movable member and said adjustable input being adjusted to apply a low selected current signal to said output line which is indicative of a zero position of the movable member;

a span adjust amplifier having an input connected to said output of said zero adjust amplifier, said span adjust amplifier having an output and being connected to influence a current on said output line, said span adjust amplifier having an adjustable input, said movable contact being movable to maximum position corresponding to a maximum position of the movable member and said adjustable input of said span adjust amplifier being adjusted to apply a high selected current signal to said output line which is indicative of the maximum position of the movable member;

a voltage-to-current stage connected between said input and output lines and connected to said output of said span adjust amplifier for converting a voltage signal from said span adjust amplifier to current signal on said output line; and

a system controller having a resistive load connected between said other terminal of said power supply and said output line, said controller connected to a M/P converter for controlling said actuator device.

8. The combination according to claim 7, wherein said M/P converter comprises an electro-pneumatic converter for receiving power from said system controller and having pneumatic means for applying a variable pneumatic signal to the actuator device for controlling the actuator device.

9. A combination of a position transmitter and a system controller comprising:

a DC power supply having a pair of terminals;

an input line connected to one terminal of said power supply;

an output line connected to the other terminal of said power supply;

voltage divider means connected between said input and output lines and having a movable contact mechanically engageable with the movable member of the actuator device for carrying a voltage which varies with motion of the movable member;

a zero adjust amplifier having an input connected to said movable contact for receiving the voltage carried by said movable contact, and an output, said zero adjust amplifier being connected to influence a current on said output line and having an adjustable input, said movable contact being movable to a zero position corresponding to a zero position of the movable member and said adjustable input being adjusted to apply a low selected current signal to said output line which is indicative of a zero position of the movable member;

a span adjust amplifier having an input connected to said output of said zero adjust amplifier, said span adjust amplifier having an output and being connected to influence a current on said output line, said span adjust amplifier having an adjustable input, said movable contact being movable to a maixmum position corresponding to a maximum position of the movable member and said adjustable input of said span adjust amplifier being adjusted to apply a high selected current signal to said output line which is indicative of the maximum position of the movable member;

a voltage-to-current stage connected between said input and output lines and connected to said output of said span adjust amplifier for converting a voltage signal from said span adjust amplifier to a current signal on said output line;

said voltage divider means comprising a potentiometer resistor connected across said input and output lines, said movable contact comprising a wiper engage with said potentiometer resistor, a first resistor connected in said input line and a second resistor connected in said output line;

said DC power supply having a positive terminal connected to said input line and a negative terminal connected to said output line, a first amplifier having a positive input connected to said wiper and an output, said zero adjust amplifier having a negative input connected to said output of said first amplifier, a second potentiometer resistor connected across said input and output lines, a second wiper engaged with said second potentiometer resistor and connected to a positive input of said zero adjust amplifier, said span adjust amplifier having a negative input connected to said output of said zero adjust amplifier and having a negative feedback line having a third potentiometer resistor therein, a third wiper engaged with said third potentiometer resistor and connected to said nagative feedback line whereby said zero adjust amplifier has an adjustable input comprising said second potentiometer resistor and wiper and said span adjust amplifier has an adjustable input comprising said third potentiometer resistor and wiper; and

a system controller having a resistive load connected between said negative terminal of said power supply and said output line, said system controller connected to a M/P converter for controlling said actuator device.

10. A combination of a position transmitter and a system controller comprising:

a DC power supply having a pair of terminals;

an input line connected to one terminal of said power supply;

an output line connected to the other terminal of said power supply;

voltage divider means connected between said input and output lines and having a movable contact mechanically engageable wit the movable member of the actuator device for carrying a voltage which varies with motion of the movable member;

a zero adjust amplifier having an input connected to said movable contact for receiving the voltage carried by said movable contact, and an output, said adjust amplifier being connected to influence a current on said output line and having an adjustable input, said movable contact being movable to a zero position corresponding to a zero position of the movable member and said adjustable input being adjusted to apply a low selected current signal to said output line which is indicative of a zero position of the movable member;

a span adjust amplifier having an input connected to said output of said zero adjust amplifier, said span adjust amplifier having an output and being connected to influence a current on said output line, said span adjust amplifier having an adjustable input, said movable contact being movable to a maximum position corresponding to a maximum position of the movable member and said adjustable input of said span adjust amplifier being adjusted to apply a high selected current signal to said output line which is indicative of the maximum position of the movable member;

a voltage-to-current stage connected between said input and output lines and connected to said output of said span adjust amplifier for converting a voltage signal from said span adjust amplifier to a current signal on said output line;

said voltage divider means comprising a potentiometer resistor connected across said input and output lines, said movable contact comprising a wiper engage with said potentiometer resistor, a first resistor connected in said input line and a second resistor connected in said output line;

said DC power supply having a positive terminal connected to said input line and a negative terminal connected to said output line, a first amplifier having a positive input connected to said wiper and an output, said zero adjust amplifier having a negative input connected to said output of said first amplifier, a second potentiometer resistor connected across said input and output lines, a second wiper engaged with said second potentiometer resistor and connected to a positive input of said zero adjust amplifier, said span adjust amplifer having a negative input connected to said output of said zero adjust amplifier and having a negative feedback line having a third potentiometer resistor therein, a third wiper engaged with said third potentiometer resistor and connected to said negative feedback line whereby said zero adjust amplifier has an adjustable input comprising said second potentiometer resistor and wiper and said span adjust amplifier has an adjustable input comprising said third potentiometer resistor and wiper; and

said voltage-to-current converter comprising a transistor having an emitter and collector connected across said input and output lines, and base, a further amplifier having a negative input connected to said output of said span adjust amplifier, and an output connected to said base for controlling the conductivity of said transistor to apply a variable current to said output line with variations in voltage from said span adjust amplifier.