Hand held infrared thermometer

Hand held infrared thermometer detector is a kind of non-contact, near field human temperature detector which is popular used in many temporary and fast temperature detective needed places. With the developing of current C-Virus situation, Hand held infrared thermometer is mandatory required to use when people  in and out of the communities,public places etc. Runic as a High- tech company with high performance analog signal chain design capabilities, our product line such as OP Amps, Comparator,  Analog Switch, LDO,etc. Can  match very well with the demand of Infrared thermometers and medical equipment.

The theory of the Hand held infrared thermometer which use Analog thermopile probe’s schematic block diagram is as below:

In the picture, take battery as 9V for example,  it’s use a High-voltage LDO RS3002 transfer the battery voltage to 3V for all  the system power supply ,including MCU, LEDs, OP Amps and others. Then use a low-power consumption LDO RS3236 step down 3V to 1.5V,the function of this is to provide a reference voltage for the thermopile and which will expand the temperature detective range.In order to calculate accurate under different environment temperature, the MCU need to read the current environment temperature,and calculate through read the voltage point of the NTC resistance and the 100KΩ resistance divide voltage in the thermopile.

As the thermopile’s output resistance is high, so the topology of amplifier part suit adopt In-phase amplifier , the  magnifying power is about more than 100 times, and need reserved low-pass filter to reduce the output noise.In order to maximize the resolution of the temperature, the 1 / F noise of the OP Amp is need less than 5uVpp and the DC offset voltage is need less than 10uV. The OP Amp RS8551 in the block above is a self-stabilized, zero drift OP Amp developed by Runic technology,which has a Ultra-low offset voltage and is very suitable for DC or low frequency signal amplify. the main parameters are as below:

◆ Wide voltage supply: 2.5V~5.5V.

◆ Ultra-low offset voltage: 1uV Type, 5uV Max.

◆ Ultra-low temp shift: 5nV/C Type, 50nV/C Max.

◆ Ultra-low current offset: 50pA.

◆ Gain Bandwidth: 4.5MHz.

◆ Quiescent current: 640uA per channel.

◆ 0.01Hz~10Hz noise: 0.75uVpp.

Runic can also supply the high input voltage LDO and low input voltage LDO with excellent performance—— RS3002 series and RS3226 series.

Main features of RS3002:

◆ Wide input voltage range: 2.5V~36V, Popular used in the Common 9V battery input  application .

◆ Output current: 150mA.

◆ Ultra-low quiescent current: 2.5uA.

◆ low voltage drop: 10mA/mA.

◆ Ultra-high PSRR: 54dB/1kHz.

◆ Output voltage density optional: 1% or 2.5%.

◆ Kinds of fixed -output voltage and many packages such as SOT-23, SOT-89-3, SOT-23-5 for your choice.

Main features of RS3226:

◆ Wide input voltage range: 1.7V~7.5V, support 4 cells dry battery input application.

◆ Internal max output current limit: >500mA.

◆ Ultra-low quiescent current: 20uA.

◆ Ultra-low drop voltage :1mV/mA.

◆ High PSRR: 70dB/Hz.

◆ Output voltage density optional: 1% or 2.5%.

◆ Kinds of fixed -output voltage and many packages such as SOT-23, SOT-89-3, SOT-23-5, UTDFN-1*1-4L for your choice.