Industrial intelligent temperature control instruments have various problems due to the use of the environment (pollution, interference, vibration, etc.) in the production plant. Below, introduce the intelligent temperature control instrument common faults and troubleshooting methods.
First, the failure of the smart meter display is normal
1. The meter display is normal, but the meter does not have (4 ~ 20)mA current output. First check the transistor 5609, diode 4148 and chip resistor is normal, if it is damaged, replace it; if it is normal, check whether the DC24V power supply is normal, if not, The power supply circuit is bad. Second, check the signal output is normal, if normal, check the microcontroller control signal, if there is no signal and TL5615cp no output signal, then TL5615cp bad; if TL5615cp normal, and no amplifier output, the amplifier is bad.
2. The meter display is normal, but the internal clock does not go or travel slowly (assuming there is a printer interface)
1 Measure whether the power supply battery is 3.6V. If it is lower than 2.0V, the battery is bad.
2 Measure whether the 32.768kHz crystal oscillator is normal. You can use the test pencil to access the FireWire, pinch the crystal pin, and use the other foot to touch the end of the test pencil. If the test pencil is on, the crystal is intact, and if it is off, the crystal is damaged.
3 If the battery crystal is normal, the DS1302 is damaged.
3. The meter display is normal, but the actual control of the temperature when the overshoot if there is PID control, such failures are mostly caused by improper setting of PIV control parameters. For this kind of fault, I believe that according to the actual temperature control system, the PIV parameter should be first fixed on a value, and then observe the heating curve and continue to adjust the value until you find a suitable PID control parameter. When observing the warming curve, if the first overshoot is large, the setting of P is decreased, and if not, the setting of P is increased. If the temperature rise is very slow, decrease the setting of I, otherwise increase the setting of I; if the curve oscillates near the set target value, decrease the setting of D.
Second, the failure of the smart meter display abnormal
1. Short circuit to the thermocouple signal input. There are two main reasons for this kind of failure caused by the room temperature too high or too low:
(1) The setting of the internal cold junction compensation parameter of the instrument is too large or too small, causing the instrument to fail when it is connected to the signal.
(2) When the parameter setting is normal, it may be the key compensation circuit transistor 9014 damage.
2. When the instrument is working, the measurement value will change irregularly
(1) Insufficient connection of the temperature sensor connection or open-end welding of the measurement terminal (measuring the bridge).
(2) The instrument is subject to vibration, noise, magnetic fields, and other interference to produce this fault. Solution: Keep the signal input end away from the power line or inductive load, and do not set up in parallel with the power line. Properly ground and shield.
(3) Confirm that there is no interference source, the A/D converter ICL7135CN is damaged.
(4) If the above three items are all normal, the internal program of the MCU is confusing.
Third, the failure of the smart meter when no display
1. After power on, there is no sound inside the instrument (normal internal relay action)
Most of these failures are due to damage to the switching power supply. The specific causes are as follows:
(1) The fuse is blown.
(2) The rectifier bridge 2CW06 is damaged, resulting in no 300V DC voltage at the DC output.
(3) DC output filter capacitor leakage, resulting in voltage output less than 300V.
(4) The switching transistor TOP222Y is damaged and cannot generate high-frequency pulse voltage.
(5) Damage to the pulse transformer.
2. No display when power is on, the four work lights on the panel are on and the relay is in operation (switching power is normal)
The display block diagram of such smart meters is shown in Figure 1.
Principle: The MCU sends a binary code to display information at each moment, and sends the encoded information to the decoding circuit to decode and control the drive circuit. The display is displayed in turn from the lowest bit of the measured value display to the highest bit of the set value display. The program control refreshes at a speed higher than the resolution of the human eye to achieve complete display of information.
Repair process:
(1) The LED of each pen segment is first measured with a digital multimeter diode block (this voltage is about 3V). In normal operation, each segment of the diode should emit light.
(2) The display is normal. Measure the power supply voltage of the driving circuit and whether the driving transistor is normal. If it is normal, the rear pole will be faulty.
(3) Measure the decoding circuit and determine if the control terminal is at a normal low level. If not, it is a microcontroller failure. When it is normal, it is considered that the encoded information is sent and the corresponding decoding information is output. Decoding circuit as a 3-8 decoder when the truth table, as shown in Table 1.
If the corresponding information is output, the decoding circuit is normal, otherwise it is damaged.
(4) Use an oscilloscope to observe the waveform of the encoded information sent by the MCU. The waveforms of C, B, and A in normal conditions are shown in Figure 2.
Only three levels are not necessarily at the same time the level of change in the level, if there is no such waveform, the microcontroller is damaged.
Of course, there are many faults in the use of smart instruments (such as open welding, short circuit, virtual connection, etc.), requiring maintenance personnel to carefully look for, to troubleshoot.
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