1045 User Guide
3
The sensor is configured to continuously transmit the temperature of the measured object every 32ms.
Board Temperature
It is very important to understand that these accuracies are only guaranteed and achievable when the sensor is in
thermal equilibrium and under isothermal conditions (there are no temperature differences across the sensor package
board. The accuracy of the thermometer can be influenced by temperature differences in the board induced by causes
like (among others): Hot electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold
object very close to the sensor that not only heats the sensing element in the thermometer but also the 1045 board.
The 1045 assumes that the ambient temperature has settled to a constant temperature. If the surrounding temperature
is constantly changing, or if there is a difference of temperature across the sensor package, additional infra-red
radiation will be sensed which can result in temperature errors outside of the calibrated errors.
Emissivity
In order to measure temperature using infrared radiation, it is absolutely essential to know the emissivity of the
surface being measured. Emissivity is a measure of how effective a surface is at radiating energy. An emissivity of 1
is the most effective radiator - for a given temperature, it will radiate the most heat. The 1045 assumes that the
surface being measured has an emissivity of 1. If the 1045 is used to measure a surface with an emissivity of 0.5, the
measured temperature will be 50% of the difference in temperature between the board and object.
A few examples of some materials with a large difference in emissivity are aluminum, with a typical value of 0.18,
and plastics, which can have a value ranging from 0.85 to 0.95. The visible colour of the object does not necessarily
mean it has a higher emissivity value. A heavily oxidized aluminum object has an emissivity value of around 0.3,
even though it looks very dark. The closer the value is to 1, the better the object is at emitting radiation.
The 1045 is calibrated for an object emissivity of 1.
For an arbitrary emissivity, the measured temperature can be converted to the surface temperature using this formula:
Surface Temperature = (Sensor Temperature - Ambient Temperature) * Emis Ambient Temperature
A good resource of emissivity values of different materials can be found on this site
[2]
.
Emissivity is a complicated topic, as it can vary depending on the temperature of the material. For precise
measurements, you may have to calculate the emissivity of your material by comparing the reported Sensor
Temperature to the actual surface temperature measured with a contact thermocouple.
IR measurements are true surface temperature measurements. For example, when measuring the temperature of a
person, the actual temperature measured by an IR thermometer will be temperature of the clothing and not the skin
temperature. Emissivity of the clothes is another issue that has to be considered.
Sunlight Immunity
The Temperature Sensor also contains a built-in optical filter to cut off the visible spectra and increase immunity
against errors introduced by any surrounding light sources.
The wavelength pass band of this optical filter is from 5.5 to 14μm.
API
We document API Calls specific to this product in this section. Functions common to all Phidgets and functions not
applicable to this device are not covered here. This section is deliberately generic. For calling conventions under a
specific language, refer to the associated API manual in the Quick Downloads section for that language. For exact
values, refer to the device specifications.