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PCR beginner’s guide: failure analysis of PCR instrument

The PCR instrument is an instrument that is used frequently and for a very high time in the laboratory, so the failure rate is also relatively high. The faults of the thermal cycler mainly include the following categories:

1. Refrigeration semiconductor failure

The failure rate of the refrigeration semiconductor is related to the quality of the refrigeration semiconductor, the number of temperature changes (cycle times), and the waterproof of the refrigeration sheet.

The refrigeration semiconductor is the core component of the PCR machine. The refrigeration semiconductor used in the PCR machine is a semiconductor chip dedicated to the industrial PCR machine, which is mainly able to withstand large temperature changes. However, the production of these refrigeration semiconductors is semi-manual, and there is no good way to test their durability. In short, there is a certain failure rate.

The number of times the refrigeration semiconductor can withstand temperature changes is related to its material and production technology. Such as ceramic chip dicing, non-hard welding and other technologies. Good refrigeration semiconductor manufacturers will provide experimental data on the number of temperature changes. Its performance will decrease with the number of temperature changes. Some PCR machines have the function of counting the number of temperature changes.

When the cooling fins are kept at a low temperature (such as 4 degrees), the cold noodles will condense water. Therefore, the refrigeration semiconductor chip needs to be waterproof (the manufacturer charges for this process), and the surrounding environment also needs to be waterproof. If the waterproofing is not done well, the life of the cooling semiconductor chip will be greatly reduced if water enters the cooling semiconductor chip. Users of PCR machines in southern China often experience refrigeration sheet failures after overnight stays at 4 degrees Celsius. Therefore, if you do not need to stay overnight at 4 degrees, it is best not to stay overnight at 4 degrees.

2. Temperature sensor failure

There are roughly three types of temperature sensors used in PCR machines, namely thermal resistance type, thermocouple type and semiconductor type. Thermal resistance type and thermocouple type are used more and have a lower failure rate. The failure rate is higher when used in the instrument (of course it has other advantages). Some PCR machines will report sensor failures. In fact, the sensor, sensor-related wiring and sensor signal processing circuit failures are all possible.

3. The control board is faulty

The control board is the command center of the PCR instrument, and it is more susceptible to failures caused by external factors, such as excessive dust causing excessive temperature of the control board, excessive humidity causing short circuits, crosstalk (from the power cord), and electromagnetic radiation (Wireless) interference, etc. Imported PCR machines generally have a low failure rate in developed countries such as Europe and the United States, but a high failure rate in China. The main reason is that the dusty laboratory environment in the north of China and the high humidity in the south are not considered.

4. Power board failure

The power board failure mainly comes from the poor quality of the power supply (the price of different levels of power supply varies greatly) and the poor power supply environment. The failure rate of the power supply of the low-end PCR instrument is relatively high, and its tolerance to poor power supply environment is poor, such as large voltage fluctuations and insufficient anti-interference ability such as clutter.

5. Hot cover failure

The thermal cover is generally maintained at about 105 degrees during operation. As far as I know, it can be roughly divided into three types: electric heating film type, electric heating wire type and circuit board type. The cost of the electric heating film type is lower, but its adhesion to the metal plate of the heating cover and the lead of the electric heating film interface are difficult to make Good, so the failure rate is higher. The heating wire type is to bury the heating wire in the middle of the thermally conductive silicone plate and paste it on the metal plate of the heat cover with glue, and the failure rate is also higher.

6. Software failure

The so-called software bugs, etc., are generally eliminated through software updates.

7. Other failures

Such as component failure, poor welding, etc.

Among them, the first three types of failures, namely, the maintenance of refrigeration semiconductors, temperature sensors, and control board failures will affect the temperature performance of the PCR instrument. It is necessary to use a special multi-temperature probe thermometer and supporting software for temperature measurement and temperature calibration. The manufacturer completes. I will elaborate on it later.