Heimann Sensors Review
From IPVM members only article Aug2020 – IPVM released article covering Heimann. Heimann is one of the two main thermopile sensors (aka infrared) suppliers. China buys Heimanns and Melexis for use in its temperature tablets. Those are typically complemented by a camera and some software which typically highlights AI in the first sentence. These tablets generally retail on China markets for sub-1000 but there are relabelers in the U.S. charging much higher. KMA is a member of IPVM.
Heimann Sensors Article Excerpts:
Many fever tablet suppliers market German-made Heimann thermal sensors while the company touts its “Essential role in fighting the pandemic”.
We spoke with Heimann Sensor, and in this report, we examine:
- Who is Heimann Sensor
- What type of sensors Heimann offers
- Are Heimann sensors accurate for medical applications
- How are thermopiles different from microbolometers
- Worldwide demand causing long lead times
Heimann Thermopile Sensors
Heimann offers a wide range of low-cost thermal devices called thermopile arrays in 6 common pixel-size variants from 8×8 to 80×64. Heimann arrays list price ranges from $19 to $270 USD per device. The most common sensors specifed by low-cost fever tablet suppliers are 32×32 or 16×16 and sell for ~$40 for quantities of 200 or more.
Thermopile Versus Microbolometers
The advantages of thermophiles include lower cost and no calibration; however, the disadvantages are lower resolution and less sensitive to variances in temperature. Heimann said that thermopiles are thermally stable and do not drift, unlike microbolometers, so they do not require continued calibration:
From the technical side, thermopiles are stable over time and don’t drift like microbolometers. Devices that drift have to include some method for re-establishing zero. This normally requires a shutter and its mechanism. Re-establishing zero is referred to as
“non-uniformity correction”, sometimes abbreviated as NUC. In this process, the shutter is closed, the electronics tells the microprocessor that there is no infrared input and everything is re-set to zero. Then the shutter is opened, and the measurement is made. However, as soon as the shutter is opened, the microbolometer starts its slow drift again. The NUC has to be performed regularly. From what I have seen, this happens every few minutes.
Thermopiles are less sensitive than microbolometers, are slower to detect changes in temperature, and because of the lower pixel count require a much smaller FoV to have the same pixel spot size.
Heimann said that thermopiles are less expensive and less complex:
From the economic side, thermopiles are less expensive than the microbolometers, which have to include the cost of the shutter assembly.
Not Medical Accuracy Calibrated From Factory
Heimann’s said their factory-calibrated accuracy typically offers ±1 – 2°C over a wide temperature range, and “higher accuracy” near body temperature, but cannot o er medical-grade accuracy calibration:
Notably, many China-made fever tablets market high accuracy performance, ±0.3°C, at 1′-3′ from the tablet. While there a few claiming greater (±0.2°C) or worse (±0.54°C), there is not a wide range of accuracy claims:
IPVM testing has shown that low-cost fever tablets frequently miss elevated skin temperatures and are less accurate than marketed.
Worldwide Demand Increase Causing Supply Issues
Heimann’s US Distributor, Boston Electronics, reported that worldwide demand has created long lead times: Be aware that the worldwide demand for these products is through the roof. Lead times are very long depending upon what you want. We can give you our best estimates of product availability.
Regardless of tablet performance, this is clearly a boom for Heimann but IPVM is concerned about using these sensors to do fever /elevated temperature screening given the limitations of the Heiman sensors and OEMs use of compensating algorithms.
We would note in the case of FDA 510K submittals and approvals that there are none for infrared touchless temperature systems such as infrared. These devices have been adapted from the microwave, automotive (defoggers) and other industry uses.