Friday, February 20, 2015

Quickly Identify and Characterize Thermal Measurement Points

Being an R&D electronics engineer, have you ever wondered if your first prototype works as designed? Using your notes or experience, you can theoretically derive where the most power is dissipated and identify the potential problem areas, but a flaw in the design where power is being consumed at an unexpected rate might go undetected. A thermal imager can quickly help to identify these problem areas. Then, you can characterize your design in different scenarios using DAQ system and thermocouples.

Quickly identify thermal measurement points with a thermal imager or a thermal camera

First, you need to identify the area that you want to monitor. In traditional electronics design, this means finding hotspots or areas where you have poor air flow. In other applications, such as building inspection, hot or cold spots may be area of concern. Using a thermal imager will quickly allow you to determine where to focus your efforts. Below are some samples of images and its respective thermal images that highlight areas that are relatively hotter. 

Figure 1: Picture of a printed circuit assembly (PCA) under test

Figure 2: Two thermal pictures of a PCA. Right image is a close-up portion of the left-hand portion of the PCA. 
Most thermal camera in the market will highlight the maximum and minimum temperature on the display, and some comes with the option to add spot measurements. The thermal images above shows some hotspots, allowing us to determine where to focus our efforts. To ensure you get an accurate measurement, remember to set the emissivity setting at the thermal imager to match your printed circuit board, or the material you are measuring. Emissivity of a material is its relative ability to emit infrared energy. As an example, the emissivity of normal FR4 PCB is 0.91. One other option is to spray your board with a spray-on high emissivity coating, such as boron nitride lubricant, that has an emissivity value of 1.

Making data acquisition temperature measurements

Once the points have been determined, a DAQ system can be used to further characterize the heat profile of your design. One of the first steps to characterizing your temperature is to choose the right temperature sensor. Common temperature sensors include thermocouples, Resistance Temperature Detectors (RTDs), thermistors, and IC sensors. Each has its own particular advantages for different applications.

Once you have decided on the type of device to use for temperature monitoring, you will need to mount the devices onto your board or structure. Once your system has been wired and mounted, you can do a long term monitoring of your design in various environmental conditions, under real-world conditions or in an environmental chamber.

Using a thermal imager, you can quickly identify thermal points that you want to monitor. With DAQ system and temperature sensors, you can make reliable, accurate and long-term temperature measurements to fully characterize your designs. With a thermal imager and a DAQ system, performing temperature measurements on your designs has never been easier. 

For more information on this application, click here to read on. 

Tuesday, February 3, 2015

HV cable insulation resistance test for hybrid vehicle

Figure 1 Toyota Prius, one of the most recognized hybrid cars on the road
Toyota Prius is among the first hybrid cars in mass production. The Toyota Prius is the world's bestselling hybrid car, with cumulative global sales of over 3 million units.  It was designed for fuel efficiency and ultra-low emissions. A hybrid electric vehicle (HEV) is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric power train is intended to achieve either better fuel economy than a conventional vehicle or better performance.
The hybrid control system combines the best operating characteristics of the combustion engine and electric motor depending to the driving condition.  Prius adopts the sophisticated Toyota Hybrid System (THS/THS II*). The system essentially is an energy recovery mechanism which slows down a vehicle or object by converting its kinetic energy to supplement the power of fuel burning. This contrasts with conventional braking systems, where the excess kinetic energy is converted to heat by friction in the brake linings and therefore wasted.  This system therefore helps to achieve superior fuel efficiency and reduction of CO2 emission.
* The THS II developed under Toyota’s “Hybrid Synergy Drive” concept, the refinement of the original Toyota Hybrid System. 

The hybrid system consists of the following main components:
  • Gasoline engine – engine runs to drive the wheels during normal driving and at acceleration
  • Motor generators (MG) – generate electrical power and recharge HV battery
  • Power Split Device – split the torque between the motor generators and engine.
  • Inverter system – converts high DC voltage (HV battery) to AC (MG) and vice versa
  • HV Batteries – supply electric power to Motor generator during start-off, low speed, acceleration and uphill driving.

The hybrid vehicle operates at high-voltage system up to a few hundred volts. The high voltage system includes the HV battery, inverter assembly and the motor generators. They are connected with the high voltage power cable in orange color. Any leakage in high voltage insulation system may lead to shorter HV battery life. It may be harmful to the human body if accidentally touched. To check the HV cable insulation integrity, the hybrid vehicle service technicians use insulation resistance tester to measure the insulation resistance between the power cable and body ground, and compare the test result with the manufacturer recommended limit. Sometimes, contamination or moisture may lead to low insulation resistance reading. 
Figure 2 Testing the insulation resistance value between the HV power cable and the body ground.  The Keysight U1461A insulation multimeter shows >260 GΩ, indicates the insulation is in good condition.