Digital temperature controller

• US 4,056,708 A
• Filed: 07/22/1975
• Issued: 11/01/1977
• Est. Priority Date: 07/22/1975
• Status: Expired due to Term

• Current Assignee: Technicon Instruments Corporation (Bayer AG)
• Original Assignee: Baxter Travenol Laboratories Incorporated (Baxter International Inc.)
• Inventors: Gelbman, Alexander, Soodak, Charles
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Bell, Fred E.
• Application Number:
  US05/598,037
• Time in Patent Office: 833 Days
• Field of Search: 219/490, 219/494, 219/497, 219/499, 219/501, 219/506, 323/19, 323/225 C, 323/68, 340/172.5, 233/11
• US Class Current: 219/499
• CPC Class Codes: G05B 11/28 using pulse-height modulation; using pulse-width modulation
• CPC Class Codes: G05D 23/1913 delivering a series of pulses
• CPC Class Codes: G05D 23/1917 using digital means
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor

Abstract

A temperature control assembly for a centrifugal chemical treatment apparatus of the type having a temperature monitoring thermistor and a rotor heater. The heater is energized from a power source through a solid state relay. The thermistor is connected in a temperature Wheatstone bridge which delivers a voltage signal to a digital voltmeter. The digital voltmeter generates a binary output which is compared in a computer with a digital command signal from a keyboard unit. The binary computer output is a programmed function of the difference between the keyboard digital temperature command signal and the voltmeter output. This computer output controls a variable duty cycle multivibrator stage which provides a relay-operating signal whose "on" time is in accordance with the difference between the keyboard command temperature and the digital voltmeter output signal. This operating signal is delivered to the relay via an over-temperature and failure detector receiving signals from the digital voltmeter. The relay is held open if forbidden signals are received, such as signals of incorrect polarity, over-range signals, signals resulting from a meter defect, signals resulting from a shorted or open thermistor, or the like. The same reference voltage is used for the digital voltmeter and the temperature Wheatstone bridge so that changes in reference voltage do not affect the voltmeter readings. The bridge is designed so that the bridge output in volts is equal to 1/100 of the temperature in degrees Centigrade to facilitate display, over the specified design temperature range. The voltmeter is of a type providing forbidden signal outputs, including over-range, wrong polarity, overload, etc.

Claims

1. A chemical treatment apparatus including temperature control means comprising heater means, an electrical power source, circuit means including a relay device connecting said power source to said heater means, temperature sensing means including a temperature sensor in the apparatus generating a signal corresponding to actual temperature, temperature command means furnishing a command signal corresponding to a desired temperature, programmable computer means connected between the sensing means and the command means generating a control signal which is a programmed function of the difference between the desired temperature and the actual temperature, means operating said relay device in accordance with said control signal to control the supply of power to said heater means and modulate the supply in accordance with said programmed function, temperature indicating means connected to said sensing means, said indicating means having means to provide an output signal corresponding to said actual temperature, wherein said computer means is connected between the output of said indicating means and said command means, wherein said temperature indicating means comprises a digital voltmeter and said output signal is in binary form, the command signal being likewise in binary form, and wherein said digital voltmeter includes terminal means to supply the binary actual temperature output signals and means to supply additional signals representing abnormal system conditions, and means to inhibit operation of said relay device responsive to the presence of any of said additional signals or to the absence of actual temperature output signals.

2. The chemical treatment apparatus of claim 1, and means to inhibit operation of said relay device responsive to an actual temperature signal corresponding to a value above a predetermined limit.

3. The chemical treatment apparatus of claim 1, and wherein said inhibiting means comprises a first OR gate receiving said additional signals, a first AND gate including respective inverters at its inputs receiving said binary actual temperature signals, a second OR gate receiving the outputs of said first OR gate and said first AND gate, said second OR gate being provided with an inverter at its output, duty cycle adjusting means receiving the output of said computer means, a second AND gate receiving the inverted output of said second OR gate and the output of said duty cycle adjusting means, and circuit means operatively connecting the output of said second AND gate to said relay device.

4. The chemical treatment apparatus of claim 3, and wherein said relay device comprises a solid state relay and wherein said last-named circuit means comprises a switching transistor connected between the output of said second AND gate and the gate electrode of said solid state relay.

5. The chemical treatment apparatus of claim 3, and wherein said chemical treatment apparatus is of the centrifuge type having a rotor comprising a treatment vessel and wherein the heater means and the temperature sensor are mounted on the rotor.

6. The chemical treatment apparatus of claim 5, and wherein said temperature sensor comprises a thermistor and the temperature sensing means comprises a Wheatstone bridge with the thermistor forming an arm of the bridge.