Digital display instrument fault inspection and treatment methods

There are a large number of display instruments in use in industrial sites, and troubleshooting of display instruments is a problem faced by users. This article introduces the fault judgment ideas, fault inspection methods and troubleshooting of the display instrument itself to help everyone improve their ability to deal with display instrument faults.

1. Fault diagnosis ideas for display instruments

When measuring parameters such as temperature, pressure, flow, liquid level, etc., display instruments are mostly used to display the control or recorders are used to record the measurement results. When the display instrument fails, the failure symptoms include: some instruments will not move, display maximum or minimum, large display error, slow response of the instrument, large fluctuations in the display, etc.

The reasons why the display instrument will not operate include interruption or input signal interruption. This is easier to check and judge. When displaying the maximum or minimum value, you need to check whether the input signal is normal. If the thermal circuit is blocked, the instrument will already display the maximum value. The display instrument has a burnout protection circuit. When the thermocouple is broken, the instrument will display the maximum or a set temperature value. If it is a display used in conjunction with a transmitter, when the transmitter has no signal output, the display will mostly display the minimum value. For large display errors, if the errors caused by the measuring components are eliminated, the display instrument itself should be calibrated. When the displayed value fluctuates greatly, you should first check whether the wiring is loose and whether the line contact is good. If it is determined that there is no problem with the line, you should consider whether there is interference.

When the display instrument has no display or cannot work normally, the digital display instrument and paperless recorder must first consider the parameter setting (i.e. program setting). Especially for new instruments, it is also necessary to check the parameter setting issues for instruments in use. If the measurement or control parameters are not correctly set, the instrument will not work properly. Therefore, when analyzing and judging faults, you should first check whether the parameter settings are correct, and then check for hardware problems.

2. Examples of troubleshooting and handling of display instruments

①Parameter setting of digital display

Most of the digital display meters used today use microprocessors, and manufacturers call them smart meters. Compared with traditional front digital displays, the biggest difference is that the use of smart meters is based on parameter settings. Therefore, when judging and handling this type of instrument failure, you must understand the working status of the instrument, because its working status will determine whether you can perform a certain operation. The instrument in normal use is usually in the basic state and the basic state or program running state can be achieved by pressing the button.

Digital display instruments have different parameter setting methods due to different manufacturers and models. However, due to the limited panel size of the instrument, the most popular buttons on digital display instruments usually include the following four:

In the basic state, press and hold the key for 5 seconds to enter the parameter setting state. In the parameter setting state, press the key again, and the instrument will display each parameter in turn; use the key to modify the parameter value. Press and hold the key to return to displaying the previous parameter. Long press the button to exit the parameter setting state. If there is no key operation after 30 seconds, the instrument will automatically exit the parameter setting state and return to the basic state.

②Fault judgment and treatment of digital display instrument

Due to the use of microprocessors and integrated blocks, as well as software zero-point correction technology, today's digital display instruments have high reliability and the probability of instrument failure is still low. Many faults are caused by external reasons and incorrect parameter settings. The following are examples of fault judgment and processing of yr-gfc series display controllers.

a. The instrument does not work, and the displayed value will not change with the measurement signal.

You should first check whether the input wiring of the instrument is correct. On this basis, check whether there are any problems with the parameter settings. For example, whether the input type setting of the instrument matches; whether the input range upper and lower limits, decimal point position, amplification factor, zero point shift correction and other parameter settings are correct. Common problems are mixing up the thermocouple and the thermal resistor or connecting the wires wrongly, etc.

b. The instrument can work, but there is no output signal

You should first check whether the instrument output wiring is correct, and then check whether the parameter settings, such as control mode, output mode, and output upper and lower limit settings, are correct.

c. The meter displays "-oh-" and flashes

Indicates that the input signal exceeds the instrument range. You should first check whether the input sensor is damaged; whether the input wiring is correct; whether the instrument input type setting matches the sensor; whether the instrument input range setting is consistent with the sensor range; whether the amplification ratio and zero point migration correction and other parameter settings are correct.

d. The display value of the instrument fluctuates greatly.

From a common sense point of view, the reasons for the large fluctuations in the instrument display are: first, the input wiring is in poor contact, or the protective sleeve of the thermocouple has leaked and is about to be damaged; second, there may be interference. After eliminating the cause of the contact problem of the wires and the thermocouple protection sleeve, the interference problem should be focused on. For example, whether the signal lines coming from the scene use shielded wires or take shielding measures. For thermocouples, check their internal insulation, whether the thermocouple electrodes collide with the metal protective sleeve, etc. For electric furnace temperature measurement, attention should also be paid to the reason why the leakage of insulation materials at high temperatures affects the thermocouple, causing the measurement value to fluctuate.

e. The given value sv and internal parameters of the instrument cannot be modified.

This is because the parameter lock of the instrument has taken effect, so that you have no right to modify the given value sv and internal parameters of the instrument. In order to ensure the safety of the control system and prevent irrelevant personnel from tampering with the instrument, most digital displays have a parameter lock function. For example, the setting of the parameter lock "loc" of the yr trademark series instruments has levels. When loc is set to a value other than "0" and "132", the instrument cannot modify any parameters; when loc is set to "0", the first-level parameters of the instrument can be modified; when loc is set to "132" , you can modify all parameters of the instrument; but after modifying the parameters, it is recommended to set loc to other values ​​other than "0" and "132".