The principle of operation of digital thermometers is based on measuring the voltage drop in a DC circuit of a set value on a thermally dependent resistance included in it.
A platinum thermocouple is used as a thermosensitive element, the resistance value of which at a temperature of 0 ° C is 1, 000 ohms. The platinum element is connected to a DC power supply circuit with a calibrated value of 1 mA.
The scale converter, switched on according to the inverting amplifier circuit, compensates for the voltage drop across the thermocouple at a temperature of 0 ° C, as well as the large-scale conversion of the useful signal to the operating level of the analog-to-digital converter (hereinafter referred to as the ADC).
The processor performs general synchronization and operation of the digital indicator, and also ensures the organization of a calibrated DC value in the source by applying a reference voltage of 2.5 V.
A four-decade LED indicator is used as a digital indicator, which ensures the normal operation of thermometers at a temperature of minus 50 ° C.
Structurally, thermometers consist of a measuring unit and a temperature sensor connected by a 15 m long cable.
The measuring unit is made in a sealed metal case, on the lid of which there is an LED indicator and a power switch.
The case has a separate compartment for the power supply and a socket for charging the battery of the power supply during operation.
The body of the temperature sensor is a thin metal tube made of stainless steel.
The cable entries are sealed.
The level " 0" Of the explosion protection of the meter is provided by the type of explosion protection " Intrinsically safe electrical circuit " Ia" According to GOST 30852.10-2002" . The explosion protection label is " 0ExiaIIBT4" .
Thermometers can be used in various industries, including explosive gases, to measure the temperature of liquid substances, with the exception of chemically aggressive media (solutions of acids, alkalis, etc. ).