Fault analysis and treatment of temperature transmitter

Fault analysis and treatment of temperature transmitter


Temperature transmitter is widely used, because of the environment, the scene, and the matching instruments vary widely, engineers, technicians or maintenance personnel encountered a variety of problems in the process of using. Here, the author combines years of work experience, a brief analysis of several major causes of temperature transmitter failure.
1, temperature sensor caused by the fault
This is the most common and best judged fault. In use, once the temperature transmitter output is abnormal, check the temperature sensor for failure first. In the case of normal temperature transmitter circuit, there are several situations.
(1) the temperature sensor is broken. The quality of the temperature transmitter has a temperature sensor fuse alarm function, at this time, regardless of the transmitter front is connected to thermal resistance or thermocouple, will show that the transmitter output value is less than the standard signal, that is less than 4mA. The current standard of fuse alarm current is 3.75mA, when the test output temperature transmitter, 000 with the current meter display value is 3.75mA, while the transmitter module red light flashing, you can determine the temperature sensor circuit, the front end of the probe can be replaced to solve.

Some customers because of differences in the instrument, the fuse alarm current with special requirements, manufacturers can be customized, such as requiring fuse alarm current is less than 3mA, in the case of ensuring accuracy can reach 2.95mA, or even lower.
(2) the temperature sensor is short circuited. At this point, the temperature transmitter output value is generally not regular, is an abnormal value, can be understood as the software “ garbled ”. In fact, due to the temperature sensor circuit, the voltage across the constant current source excitation into the microcontroller may be abnormal voltage value, and then after a series of AD conversion, amplification, DA conversion, the final output is a non normal value. If the front circuit is well handled, the temperature transmitter module will not be damaged, and the damaged circuit will damage the module.
(3) &ldquo temperature sensor; virtual open area ”. This situation is usually the temperature transmitter is normal, sometimes abnormal. Most of the reasons are temperature sensor packaging quality, replace the probe can be resolved.
2 、 power supply power failure
The normal temperature transmitter has a power supply range of 9~30VDCOr, 8.5~30VDC, customers use more 12VDC, 24VDC DC switching power supply. Normally, the power supply will not cause damage to the temperature transmitter. If there is a problem with the power supply, it is very likely to damage the temperature transmitter.
(1) the power supply voltage is low. The general design of temperature transmitter power supply circuit is the left margin, if the supply voltage is lower than the standard 2~3VDC (of course, temperature transmitter with low power consumption according to different output, can do 5VDC power supply, 3.3VDC power supply, even) in order to ensure the normal power consumption under the condition of temperature transmitter, temperature transmitter can work normally. Even if the power consumption of the temperature transmitter can not be met, the temperature transmitter will not work properly and will not be damaged.
(2) the supply voltage is on the high side. In general, the maximum voltage not more than 32VDC, more than the basic damage temperature transmitter. Even if no component is burned in the lucky power circuit, its service life will be reduced.
(3) the problem of common power supply. In the system, it is common for most devices to share the same power supply. In general, the same level of power equipment will be the basic well afraid system has high power equipment or continuous stop equipment, light will cause the charge accumulation caused by interference, will produce surge. Therefore, engineers in the design of the circuit, it is best to specifically analyze the equipment and instrumentation used, different types of equipment, instruments and meters separate power supply, so that no interference, mutual influence.
3, the surge of disaster
Surge is the most common and biggest black hand that damages the temperature transmitter. Check out the Baidu encyclopedia and 360 encyclopedia, the definition of surge is as follows. Surge is also called surge, as the name implies is beyond the normal working voltage transient overvoltage. In essence, a surge is a violent pulse that occurs within just a few minutes of a second. Possible causes of surges include heavy equipment, short circuits, power switching, or large engines. With the surge block device products can effectively absorb huge energy burst, in order to protect the connected device from being damaged.

After reading the above definition, I will not elaborate on the lethality of the surge, you should feel the damage estimation of temperature transmitter is normal! If your system or equipment in the above conditions exist, not only to choose isolated type of temperature transmitter, but also to do a variety of grounding, insulation, shielding, protective circuits and other protective measures. Because in addition to the temperature transmitter, other devices in the system may not survive the surge disaster.
4, electromagnetic interference trouble
Large motor, large machinery, reactor, power equipment, transmission lines, radio, and even occasional large equipment can generate electromagnetic fields, the basic will have electromagnetic conduction or radiation, electromagnetic interference is complicated, variety, no way to the utmost. Therefore, experienced engineers or technicians should carefully analyze their own site environment and take necessary measures. In the beginning of the design, the electromagnetic interference as the focus of prevention, so as to nip in the bud, and strive to reduce the subsequent use of the process of trouble.