Download Conductivity

BMED 4490 Sensors & Instruments
01/29/01
Class Exercise #2
Class Exercise #3
Objective:
Use conductivity to detect holes in gloves in O.R.
Concept:
Use a voltage divider in which the conductivity of holes in the glove are detected
as a change in resistance.
Equipment:
Signal generator
Differential amplifier
Narrow band filter(s)
Oscilloscope
Gloves and electrodes
Teams
Gloves/electrodes:
Safety:
Filters/Scope:
Diff Amp:
1
BMED 4490 Sensors & Instruments
01/29/01
Class Exercise #2
Filter Design
1. Look at filter frequency response and estimate the undamped natural frequency
and damping coefficient. Also check the stability.
2. Check out noise at the input and output of the filter. Is the noise less at the output,
why or why not?
3. Find the transfer function from the schematic.
4. Determine the relationship between the variable resistances and the values for the
damping coefficient and the undamped natural frequency. The variable
resistances associated with OA3 and OA4 should be used to adjust the undamped
natural frequency.
5. Find or calculate (e.g. PSpice) the frequency response function magnitude and
phase for small damping coefficient
6. Predict how the damping coefficient will affect noise power.
7. Consider the effect of sinewave frequency drift on determining damping
coefficient.
8. Use the supplied filter chip, design a filter.
Electrical Safety
1. Use the electrical safety analyzer to determine some of the parameters of
electrical safety. Consider improving power cord resistance test results.
2. Use the electrical isolation transformer and repeat the test.
3. Consider the sinewave voltage applied to the circuitry. What are safe levels of
sinewave voltage? Assume R = 1 megohm.
4. What other design considerations should be implemented for electrical safety.
Consider the electrical isolation of the surgeon (e.g. insulating or conductive
shoes, skin), and static electricity. Consider use of staticide.
Gloves/Electrodes
1. Put the electrodes in saline; no glove try 200Hz, 2KHz, 20KHz. What is the
resistance?
2. Put a large hole in the glove; measure the size; such that the result is different
from electrodes in saline alone.
3. Estimate glove z, R
4. Predict the relationship of z, R to hole size
5. What are the limits on z measurement due to the presence of the physician
Bridge
1.
2.
3.
4.
5.
6.
Minimize CMRR using VBC =0
Measure for CMRR calculation
Find response when surgeon is present using Lissajou figure
Estimate noise level
Calculate CMRR
In the absence of a hole, what is the characterization of the noise?
2
BMED 4490 Sensors & Instruments
01/29/01
Class Exercise #2
Safety Data
For function generator, filter and differential amplifier
-- each utilizing a separate power supply.
1. Self test of analyzer = 1001
2. System voltage
L1-L2 =120.6
L1-Gnd =0.2
L2-Gnd = 120.5
3. Power Cord Resistance
639 milliohms
4. Case leakage: external lead (microamperes)
Power On: Normal Polarity:
Open 31.4
Close 0.0
Reverse Polarity
Open 27.5
Close 0.0
Power Off: Normal Polarity:
Open
Close
Reverse Polarity
Open
Close
33.7
0.0
25.3
0.0
5. Case leakage: ground conductor (microamperes)
Ground open normal
33.5
Reverse
25.1
3