US 4,399,428 AGranted

Thermostat

AssigneeUnited Brands Company

InventorsPaul R. Hughes, John E. Campbell

Life of this patent

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Abstract

A thermostat monitoring and controlling the temperature of produce ripening within an enclosure and featuring a bridge circuit sensing errors between the actual and desired temperatures in which the desired temperature is selected directly in units of degrees. A bridge amplifier having feedback maintains the bridge in electrical balance to avoid errors due to changes in bridge component self heating. An error detection circuit having a single control simultaneously selects upper and lower error limits centered on the desired temperature, in units of degrees. The circuit indicates whenever the actual temperature goes outside these limits. An alarm circuit indicates a temperature error or a power failure in the thermostat at the thermostat and at a remote location. This circuit utilizes an alternating current source which activates current direction-dependent indicators operating on alternate half cycles. Electrical isolation of the temperature monitoring circuitry from the circuitry controlling heating, cooling and fan equipments is provided by coupling a signal indicating a temperature error through a single electrically isolating interface to equipment selection and control circuitry at line potential.

Claims8

Dependent claims

A device for monitoring and controlling the temperature of products within an enclosure comprising:

a bridge circuit having as a first leg a temperature sensing, self-linearizing network that includes a thermistor arranged with a plurality of resistors, one in series and one in parallel with said thermistor, said network establishing a substantially linear overall conductance curve for said first leg over a temperature range of interest, and a digital set point selector network in a second leg of said bridge circuit to select digital values of the temperature over said range of interest, said set point network comprising:
a set of conductances, said conductances being connected in parallel with one another, each said conductance of said set having a switch element in series with it, and a further conductance in parallel with said set of conductances, said further conductance having a value to establish a first conductance limit of the selector network when all of the conductances in said set of conductances are switched out of said network thereby to define a bridge balance point at one end of said temperature range of interest, the values of said conductances of said set being predetermined to establish, by selective switching, a series of decimal temperature bridge balance points over said linearized portion of said conductance curve of said sensing network thereby to establish a progressive series of temperature set points in decimal steps;
a bridge amplifier connected to the bridge circuit to generate an error signal output when the sensed temperature of said temperature sensing self-linearizing network differs from the selected temperature of said digital set point selector network;
and signaling means responsive to the amplifier error signal output for giving warning or signaling correction to temperature control means.

1 more element

A temperature monitoring and control circuit for monitoring the temperature of products within an enclosure which can have various critical temperature characteristics, comprising a reference network that provides upper and lower signal outputs and a bridge reference signal output, the value of said bridge reference signal being intermediate the values of said upper and lower signal outputs, said reference network forming a bridge reference branch,

a bridge circuit formed by a temperature sensing branch and said reference branch, said temperature sensing branch providing a temperature signal output,
said bridge circuit including means to vary a desired set point temperature at which said outputs are equal,
a bridge amplifier having as inputs said temperature signal and reference signal outputs and constructed to generate an error signal output dependent upon the difference between said inputs, a temperature control means responsive to said error signal, effective to change the thermal condition in said enclosure in a sense to reduce said error signal,
an error sensing alarm-activating circuit which includes upper and lower detectors, each detector having a function of said error signal as one input and said upper and lower signal outputs from said reference network as respective second inputs, each detector having an output serving as an alarm-activating signal, respectively for upper and lower danger conditions, and
control means connected to selectively adjust said error sensing alarm-activating circuit to vary simultaneously the effective thresholds of both of said detectors thereby to enable variations of the size of the error signal required to establish an alarm-activating condition in a manner that is independent of the set point temperature and of said temperature control means.

2 more elements

Dependencies are inferred from the claim text.

Facts

Application: 06/115,413Filed 25 Jan 1980 · division
Priority: 2 Mar 1978
Granted: 16 Aug 1983
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

G08B 17/06
Fire alarms; Alarms responsive to explosion: electric actuation of the alarm, e.g. using a thermally-operated switch
G05D 23/1902
Characterised by the use of electric means: characterised by the use of a variable reference value
G05D 23/24
With sensing elements having variation of electric or magnetic properties with change of temperature: the sensing element having a resistance…
G08B 21/182
Status alarms: level alarms, e.g. alarms responsive to variables exceeding a threshold

Family

Serial882,885Parent of this division · filed 2 Mar 1978
US 4,240,077 AParent of this division
US 4,399,428 AThis patent

From the US filing history. Foreign family members aren’t listed.

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