Download Voltage Divider/Wheatstone Bridge Lab

CENG 215
Pre-Lab Exercise
Name _____________________
Part 1 - Voltage Divider Review Exercise
1. For each of the voltage divider circuits, calculate by hand the indicated voltages.
V1
_________
VX ____________
VAB
________ VBC ______ VAC _______
VA,gnd
________ VB,gnd _________
V2, gnd _____________
V3, gnd
_________________
Voltage Divider Learning Object - review Voltage Divider and try the sample
problems
Voltage Divider Java Applet - use the Java Applet to try out various voltage divider
combinations
Voltage Divider Worksheet
do Questions 2, 3, 4, 5, 6, 7, and 8
Part 2 - Wheatstone Bridge Circuits
Single Supply Bridge Circuit
1. For a balanced Wheatstone bridge, the bridge output voltage, VAB, is ______ V.
2. For the Wheatstone bridge circuit shown, assume that resistor R4 represents a
resistive type sensor whose nominal resistance is 120 Ω. Assume now that R 4
increases to 125 Ω. Calculate by hand the bridge output voltage VAB (VA – VB)
to 3 decimal places and the current through R4.
VA = ________
VB = ________
VAB = _________
I4 __________
3. Change the value of R1 to 125 Ω also (leave R4 at 125 Ω). What is the bridge
output voltage now? VAB _________________
4. Change the value of R1 back to 120 Ω and change R2 to 125 Ω (leave R 4 at 125
Ω). What is the bridge output voltage now? VAB _________________
Part 3: Dual Supply Bridge Circuit with current limiting
1. For the Wheatstone bridge circuit shown below 2 additional current limiting
resistors have been added and a ± 12 V supply is used.
Calculate by hand:
a. The current through R4 with the bridge balanced.
b. The voltage drop from point X to point Y, VXY or VBridge.
c. Assume now that R4 increases to 125 Ω. Calculate by hand the bridge output
voltage VAB (VA – VB) and the current through R4.
d. Calculate the bridge sensitivity S (defined as the change in output/change in
input). The units will be mV/Ω.
I4 - balanced
VXY
VAB
I4 - unbalanced
Using the value of S, determine VAB if R4 changes to 135 Ω.
S
VAB ________
2. R4 is assumed to be a resistive sensor with a maximum current rating of 25 mA.
Is this sensor in danger of overheating? YES/NO Why?
Part 4: Wheatstone Bridge with Balancing Circuit
1. Calculate the range of adjustment for the balancing circuit.
Range from
____________
to
______________
2. What will happen to the range of adjustment if the 3.9 kΩ resistor is changed
to 4.7 KΩ ?
Answers
Part 1
1. V1 = 8.17 V, VX = 4 V
2. VAB = 4 V, VBC =6 V, VAC =10 V
3. V2,GND = 3.2 V, V3,GND = 5.76 V
Part 2
1.
2.
3.
4.
VA,GND = 9 V, VB,GND = 3 V
VAB = 0 V
VA = 6 V, VB = 6.122 V, VAB = - 0.122 V, I4 = 49.0 mA
VAB = 244 mV
VAB = 0 V
Part 3
I4 - balanced
21.4 mA
VXY
5.14 V
VAB
-52.0 mV
VAB = -156 mV
Part 4
1. Range 91.4 mV to – 91.3 mV
2. Range decreases 75.9 mV to – 75.9 mV
I4 - unbalanced
21.0 mA
S
- 10.4 mV/Ω