Voltage Detection Circuit Response Respective To Undervoltage Biology Essay

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Both simulation and actual hardware design was put to several tests for every stage of the sensor. Prior to the actual testing, the sensor was tested by generating simulated signals in the software. When errors occurred, the error were identified immediately and debugged. Once the particular feature was ready and confirmed, it was tested in hardware testing. It then compared with the simulation testing results. The results and findings of the measurement tests are discussed in this chapter.

SIMULATION AND TESTING

Several simulations and tests were conducted to ensure it is operating satisfactorily. Any errors are identified and being troubleshoots. The list of simulations and testing is shown in Table 4.1 Further details about the results and findings are explained in this section.

Table 4.1: List of simulation and testing conducted.

No.

Simulation and Testing

Brief Description

1

Step down transformer

To check the voltage of input and output step down transformer.

2

Rectifying

To check whether AC voltage is rectified into DC voltage.

3

Voltage Regulating

To measure constant output voltage of voltage regulating circuit which are Vcc and Vdc.

4

Filtering

To check the filtering DC voltage.

5

Smoothing

To smooth the ripple DC voltage into constant DC voltage.

6

Time Response Analysis.

To measure how fast AC to DC voltage is stabilised.

7

DC Sweep Analysis

To monitor output value of each comparators by varying input voltage, Vin.

8

Comparison of Undervoltage, Normal and Overvoltage Condition

To determine the voltage detection circuit response respective to undervoltage, normal and overvoltage condition.

9

Comparison of simulation results and actual hardware results

To determine the measurement error of the actual setup and trouble- shooting.

4.1.1 Step down transformer

Oscilloscope 1 (XSC1) is connected to the circuit as Figure 4.1. Channel A probe is connected to the primary side, while Channel B probe is connected to the secondary side of the transformer T1. The transformer T1 has ratio of primary to secondary equals to 10, which is 230VAC to 24VAC. Therefore, the purpose of this simulation is to identify the ratio of step down transformer satisfied the transformer ratio setup.

Figure 4.1: Measurement setup of step down transformer.

For initial setup, input supply voltage is set to 230Vrms which is in normal condition. Input and output waveforms of step down transformer T1 are shown in Figure 4.2. Both waveforms are in the same phase of 50Hz and primary to secondary transformer ratio is approximately to 10:1. Cursor 1 is pointed at peak voltage of the primary and secondary transformer in time 1, T1 while cursor 2 is pointed at peak voltage in time 2, T2. As the peak voltage is measured in the graph, Vrms can be calculated by dividing the peak voltage with √2.

Output

Input

Figure 4.2: Input & output waveform of step down transformer

4.1.2 Rectifying

As shown in Figure 4.3, oscilloscope XSC1 is then connected to + terminal of bridge rectifier D4, while ground is connected to - terminal of bridge rectifier D4. Purpose of this simulation, is to identify the characteristic of voltage after rectifying AC to DC voltage. As shown in Figure 4.4, the output voltage of the rectifier is in full wave DC voltage, as bridge rectifier is a full- wave rectifier. Bridge rectifier too can be replaced by four single power diodes. However, the voltages are not in pure DC voltages, in definition varies between minimum to maximum voltages. Maximum peak voltage is 23.3 V and minimum voltage is 15.1 V.

Figure 4.3: Measurement setup of rectifier for voltage regulator.

Figure 4.4: Output waveform of rectifier D4.

4.1.3 Voltage Regulating Circuit.

Measurement setup for zener diode and voltage regulating circuit are shown in Figure 4.5. Oscilloscope XSC1 is used to monitor waveform characteristic of the output voltage of voltage regulator LM7805 (Vdc) and zener diodes (Vcc), while multimeters (XMM1 and XMM2) are used to measure output voltage magnitudes. As discussed in previous chapter, zener diode used to regulate rectifying voltage into constant voltages of Vcc. Vcc is the supply voltage to LEDs and voltage comparators LM339. On the other hand, output regulator LM7805 (Vdc) is used for to set reference for over voltage and under voltage in voltage detection circuit. It is important to ensure the Vcc is approximately 15V and Vdc equals to 5V.

Figure 4.5: Measurement setup of voltage regulating circuit

Vdc

Vcc

Figure 4.6a: Waveform of voltage regulator outputs (Vcc and Vdc)

Figure 4.6b: Magnitude Vcc (XMM1) and Vdc (XMM2)

Results of the simulation are presented in Figure 4.6a and 4.6b. From Figure 4.6a, Vcc and Vdc voltage is constant through time. Moreover, magnitudes of Vcc and Vdc are 14.97V and 5V respectively. Even though Vcc is not equal to 15V accurately, it is acceptable since the voltage is sufficient for supply voltage comparator and LED. Specifically, LM339 acceptable supply voltage is between 2V to 36V. Similarly to LED used. If 12V LED is being used, 15V of Vcc is sufficient.

4.1.4 Filtering Circuit

To measure the filtering output voltage, the measurement setup is configured as in Figure 4.7. Channel A probe is connected to + terminal of bridge rectifier and the ground is connected to the - terminal while channel B probe is connected to resistor R5 to measure the voltage after filtering. Channel A and B waveform is compared to see the difference between those output voltages. The output voltage waveforms are shown as in Figure 4.8. From the graph, Va peak voltage is approximately 24V while Vb is smaller. Vb is smaller approximately by ratio of 0.1, because of voltage dividing resistors. Moreover, Vb have much less ripple compare to Va voltage waveform.

Figure 4.7: Measurement setup for rectifying and filtering circuit.

Vb

Va

Figure 4.8: Output waveform of rectifying and filtering circuit.

4.1.5 Smoothing DC circuit

To improve the DC voltage signal, smoothing DC circuit is connected by adding capacitors parallel to the resistor of the filtering circuit. It is important to ensure that output voltage of the smoothing circuit (Vin) is approximately in correct ratio. For example, 2.30Vdc is represented the 230VAC. Therefore, the measurement setup is performed as in Figure 4.9, and the result is in Figure 4.10. From the results, it is observed that the capacitor managed to smooth the DC voltage signal into pure DC after second capacitor. Ripples do exist at first smoothing circuit, but only after second smoothing capacitor, the output voltage is in pure DC signal.

Figure 4.9: Measurement setup of smoothing DC circuit

Channel A

Channel B

Figure 4.10: Output waveform of smoothing DC circuit.

4.16 Time Response Analysis.

Time response of this voltage detection circuit is measured based on how fast the voltage is stabilised from AC to DC voltage, to be input voltage of the voltage detection circuit. In voltage detection circuit, the time response is based on the comparator LM339 characteristic itself, which can be found in the datasheet. From the datasheet, LM339 response time is found to be 1.3us, which is considered as instantaneous, respective to the voltage variations.

Figure 4.11: Time Response Analysis of DC input voltage, Vin.

DC Sweep Analysis

In reference of Figure 4.12, voltage detection circuit receives supply voltage from AC to DC circuit as stated previously from previous chapter. There are two different constant supply voltages which are Vcc and Vdc. Vcc is the supply voltage for comparator and LEDs, while Vdc is used to determine the voltage reference of over voltage and under voltage limit. Vin, is the input voltage which specified ratio varied between the three main ranges depending on the condition, then, Vin is compared to the Vref of each limit.

DC Sweep Analysis is performed to monitor the output value of each comparator respective to the input voltage variations. In this analysis, input voltage, Vin is varied from 0V to 5V.The output pin of comparators are monitored as illustrated in Figure 13a,13b and 13c.

Figure 4.12: Voltage detection circuit schematic diagram

Figure 4.13a represents output voltage of pin 2, comparator U1B, which used to compare overvoltage condition. As can be seen in the figure, when Vin more than the overvoltage limit which is 2.50V, the output voltage pin 2 is low, hence current from the Vcc supply can be flow through open collector. Output voltage of pin 2 is high when Vin is less than 2.50V. Even though the high value is slightly less than 15V, current still not flowing through the open collector. Vice versa, the output voltage at pin 1, comparator U1A is low only when Vin is less than under voltage limit which is 2.15V and output is high when Vin is more than 2.15V. The response can be seen in Figure 4.13b. During normal voltage condition, which is between 2.15V and 2.50V, the output pin 13 of comparator U1D is low and when Vin is outside the normal range the output is high as shown in Figure 4.13c.

Figure 4.13a: DC sweep analysis of output comparator U1B.

Figure 4.13b: DC sweep analysis of output comparator U1A

Figure 4.13c: DC Sweep analysis of output comparator U1D

Comparison of Undervoltage, Normal and Overvoltage Condition

The next step to identify the response of the voltage detection circuit is by monitoring the light emitting diode (LED) responses respective to the variation of the voltage. In voltage detection circuit, there are three different colours which represent each voltage conditions. They are red, yellow and green; indicate overvoltage, undervoltage and normal voltage condition respectively. Moreover, it is noted that the variation voltages are defined in Vin, which are the assumptions of the supply voltage. It is assumed that the ratio of Supply Voltage: Vin is equals to 100: 1. Table 4.2 describes the results of the comparison response during overvoltage, normal voltage and undervoltage conditions. These simulation results are based on the combination of AC to DC circuit and voltage detection as shown in Figure 4.14.

Table 4.2: Voltage detection circuit responses (simulation)

Condition

Supply Voltage

(Vac)

Vin

(V)

Colour of LED ON.

Red

(Overvoltage)

Yellow

(Undervoltage)

Green

(Normal)

Overvoltage

280

2.79

√

270

2.68

√

260

2.57

√

255

2.53

√

252

2.51

√

Normal

250

2.49

√

245

2.44

√

230

2.30

√

225

2.24

√

220

2.18

√

Undervoltage

215

2.14

√

214

2.14

√

210

2.08

√

205

2.04

√

200

1.98

√

From the table, red LED is lit up during overvoltage condition is detected. Overvoltage is detected whenever Vin is more than 2.50V. Yellow LED lit up during undervoltage condition which is when Vin is less than 2.15V. When neither overvoltage nor undervoltage condition occurred, only green LED lit up indicating the supply voltage in between the acceptable voltage range; 2.15V to 2.50V. However, there is slightly difference between supply voltage and Vin, which is not satisfied the ratio 100:1. Errors and inaccuracy will be discussed in next subtopic.

Figure 4.14 Combination of AC to DC circuit and voltage detection circuit.

Comparison of simulation results and actual hardware results

It is important to test each circuit in this project to ensure it is operate satisfactorily. Beside testing and measurement in simulation software, hardware testing too is performed. In both AC to DC circuit and voltage detection circuit, resistors value play important role in voltage dividing and setting of voltage reference. Therefore, before constructing the circuits, value of each resistors used are measured as tabulated in Table 4.3.

Table 4.3 Resistors measurement

Breadboard

Printed Circuit Board (PCB)

Resistors

Actual Value (ohm)

Measurement Value (ohm)

Measurement Value (ohm)

R1

5k

5k

5k

R2

1k

1k

1.1k

R3

180k

178k

179k

R4

100

100

99

R5

10k

9.4k

10k

R6

10k

9.6k

9.6k

R7

15k

15k

15k

R8

15k

15k

15k

R9

18k

18k

18k

R10

24k

24k

24k

R11

1k

1.1k

1k

R12

1k

1k

1k

R13

1k

1k

0.99k

R14

16k

15k

14.9k

R16

100

100

Fuse

Breadboard

Printed Circuit Board (PCB)

Resistors

Actual Value (ohm)

Measurement Value (ohm)

Measurement Value (ohm)

R17

11k

9.7k

9.2k

R18

10k

10k

10k

R19

10k

10.1k

9.8k

R20

100k

99.8k

99k

As some of the resistors are not in their exact value, it is expected that there is inaccuracy during hardware testing especially in voltage detection circuit. Based on the tabulated Table 4.4, Vin might differ much from the correct value. Therefore, it affects the indication during each condition which further analyses are discussed in next subtopic.

Table 4.4: Voltage detection circuit responses (hardware)

Condition

Supply Voltage

(Vac)

Vin

(V)

Colour of LED ON.

Red

(Overvoltage)

Yellow

(Undervoltage)

Green

(Normal)

Overvoltage

280

2.76

√

270

2.65

√

260

2.55

√

255

2.50

√

252

2.50

√

√

Normal

250

2.47

√

245

2.44

√

230

2.28

√

225

2.23

√

220

2.15

√

√

Undervoltage

215

2.13

√

214

2.12

√

210

2.08

√

205

2.04

√

200

1.98

√

4.2 Problems Occurred and Trouble Shooting

First problem occurred is the connected wires are loose and disconnected internally, especially the crocodile clip wires. It caused the circuit not operated and at first it is difficult to trace the problem since the circuit is in correct configuration. After checked the wire by using the diode test of the multimeter, the problems are solved.

Second problem existed because of the effects due to very high current that not checked carefully before performing experiments. Some of the resistors can not stand high current especially resistor placed on the AC circuit. As a result, the resistor damaged but not able to trip the circuit effectively. The problem is solved by replacing the resistor value with fuse, which is safer and the circuits can be protected more efficiently. Moreover, to overcome the problems occurred again, each component is double-checked before installing in circuit construction.

Next, most of the time, the operation of circuit is interrupted due to breadboard internally connection is damaged. Internal connection of the breadboard can not be detected on the spot at the wire is connected inside and it involves with many holes of connection. However, it can be checked using diode test of the multimeter to the holes that need to be connected. In addition, for further avoidance of this error, the circuit is then implemented into printed circuit board, which the connected wire is then replaced by connected conductor, which is copper.

Besides that, inaccuracy of circuit operations existed in this project. Therefore, a few values of resistors are changed in order to increase accuracy. Plus, type of light emitting diodes is changed and buzzer is added for an enhancement.

4.3 Analysis of Experimental & Simulation Result

Having conducted several tests and simulations, it can be concluded that this project which is overvoltage sensor for industrial appliance protection could perform the voltage detection during overvoltage, undervoltage and normal voltage conditions.

However, the main downside issue is accuracy. The AC to DC circuit developed has the inability to detect transient due to the step down transformer and the voltage regulating circuit. Therefore, even though comparator LM339 has the ability to detect voltages up to 1.3us time response, due to inadequate power- supply filtering and poor grounding, this voltage detection circuit sacrifices the stability.

Also, from the results, mostly problems and errors occurred during hardware testing compared to simulation testing. The main reason is there are errors in measurement of electronic components used especially resistor. First problem occurred is the Vrms of full- wave DC voltage is smaller than expected in simulation result. Moreover the ratio Vsupply: Vin differ from the assumption of ratio 100:1. Since the ratio is not exactly accurate, the response of the voltage detection may be affected. For example, by referring to Table 4.4, when Vsupply is 252Vac, Vin is 2.50V. There are few results of testing where there is more than one LED are lit up at the same time. It occurs especially when the input voltage is between two conditions. The reason is because of hysteris occur in the typical comparator. Hysteris happen if the output voltage unable to change instantaneously respective to the variation of voltage. It can be overcome by connecting resistor parallel to output pin and + terminal of the comparator.

Error too was introduced through improper use of multimeter or power supply. On the contrary, the measurement errors when using step down transformers were very high, where the measured values were higher than actual values. The main reason might be due to amplified measurement error due to high voltage gain.

Since this project concerned to be used in Malaysia, temperature storage may not be a major issue as daily temperature is not varied drastically. However, it is noted that the important component which is LM339, has storage temperature range, which is -65°C to 150°C and its operating temperature range is 0°C to 70°C.

2.4 Operating Temperature Range.

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