Olympic Medical OLYMPIC SMART SCALE 35 Training manual

OLYMPIC
SMART SCALRtm
Model 35
Operating and Service Instructions

OLYMPIC
SMART SCALEtm
Model 35
Operating and Service Instructions
Table of Contents Page
Summary Operating Instructions.1-1
Safety Precautions.2-1
Set-Up .3-1
Operating Instructions.4-1
Service.5-1
OLYMPIC MEDICAL
4400 Seventh South • Seattle. WA 98108
Ptwne 206424.0426

Section One
Summary Operating instructions _ O lympic smart scale model 35
Weight Monitoring
Radiant Warmer or Incubator
To cancel weight of bedding
• Make bed, then press “Zero” button before placing baby on scale.
• Wait until “0” appears on display before touching scale or placing
baby on scale.
To weigh baby
• Press “Display” button to turn display on.
• Press "Gms/Lbs” button to select units.
• Press "Lock” button to lock average weight, computed during last 4
seconds, on display.
Between weighings
• Display can be turned off (or povrar disconnected) without iosing any
previous data.
• To retain last weight, leave display locked ("Read” light on).
Any Questions? Please
call Toll-Free 1-800-426-0353.
in Canada, call collect [phone]
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Page 1-1

Section Two
Safety Precautions _ O lympic smart scale model 35
1 . Do not use scale in presence of flamnnable anesthetics.
2. Connect line cord only to property grounded wall outlet.
3. Always remove incubator or radiant warmer mattress before setting
weighing platform in place
4. The scale is designed for use only with the baby confined in an incubator
or radiant warmer. Do not use weighing platform on an open table top or
for carrying the baby.
& Never permit liquid to enter the interior of the DisplayfControl unit case
or weighing platform.
a All service should be performed only by a qualified technician.
7. Always disconnect from the electrical outlet before opening the readout
case.
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Pag* 2-1

Section Three
Set-Up_
OLYMPIC SMART SCALE MODEL 35
Assembling Weighing Platform
For Radiant Warmer Use—
USE OF ADAPTER BASE
Always use adapter base with Air-Shields Radiant Warmer, Model
I.I.C.S., or any radiant warmer with opening in warmer bed.
CAUTION
Remove warmer mattress.
Place adapter base centered over opening in warmer
bed. (Fig. 3-1)
Set scale weighing platform on adapter base.
Store adapter base under scale mattress.
Do not use scale on Air-Shields Model I.I.C.S. or
any other warmer with opening in bed base without
using this adapter.
CAUTION
When using scale with opening in bed base, adapter
base must be used.
• For radiant warmer use, assemble weighing platform as
shown above, using two mattresses.
CAUTION
_Make sure bolt holding two platforms together
is securely tightened.
• Remove regular mattress from radiant warmer and place
assembled weighing platform in tray that held mattress.
CAUTION
_I Before placing platform in warmer, make sure
that the adapter base is in place over the x-ray window. If
you have any questions regarding proper installation,
please call toll-free 1-800-426-0353 before attempting to
use scale.
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Page 3-1A

USING EXTENDER TRAYS ON RADIANT
WARMER PLATFORM
For Incubator Use
All radiant warmer platforms now include adjustable extender
trays. Simply pull out trays (Fig. 3-3) once platform is set onto
radiant warmer.
CAUTION
• Extender trays should come close to edge of warmer,'
but not touch sides. If they touch, weighing errors
will occur.
• Do not set baby on extender trays
To Clean
• Remove extender trays by sliding them all the way in
the long slot, then along short slot as shown in Fig. 3-4.
Lift off.
• Clean with liquid disinfectant or mild soap and
water detergent
• Re-install trays by setting rounded end of slot over
guides (Fig. 3-4) on platform and slide along long slot to
desired width.
Fig. 3-5
• For incubator use, assemble platform as shown above.
• Remove regular mattress from incubator and place
weighing platform in tray that held mattress.
CAUTION
I If weighing platform is too large for incubator
tray, please call toll-free 1-800-426-0353 before attempting
to use scale.
Page 3-2A
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Installing Display/Control Unit
CAUTION
I Explosion hazard. Do not use scale in presence
of flammable anesthetics. (Note: Oxygen is not a
flammable gas.)
• Display/Control can be clamped to pole. ISiUllUSCl Make
sure clamp is securely tightened and that pole is stable.
• Or Display/Control may be placed on instrument shelf.
• Connect cable from weighing platform to socket on back of
Display/Control Unit. (When used in incubator pass cable
through access hole.)
• Connect power cord to properly grounded, hospital-grade
electrical outlet 115 Vac, 60 Hz.
• If the Display/Control Unit is not connected to the weighing
platform, the word "Cable” will appear on the display as a
reminder to connect them.
gSHEElThe Display/Control Unit must be used with the
samewighing platform with which it was last calibrated,
either at the factory or at the hospital. Check label on back of
Display/Control Unit for serial number of compatible platform.
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Page 3-3

Section Four
OporatinQ Instructions _ O lympic smart scale model 35
Controls and Signals
Display/Control Unit
1 . “Display On/Off” Button—Turns display (only) off
between weighings, if desired. Note: When display is
turned off, scale remembers all previous data, including
cancelled weight of bedding.
2. “Zero” Button—Has two functions:
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4. “ Gms/Lbs” Button—Changes units between grams and
pounds-ounces. Ounces are shown to nearest one-tehth.
(Example: 2 4.2 equals 2 pounds, 4.2 ounces.) Indicator
lights on display tell whether grams or pounds are being
measured.
1. Cancels out all weight on platform (mattress, bedding,
etc.) and causes display to read “0!’ Always press "Zero”
button after changing bedding and before placing baby
on scale. If baby is already on scale, lift baby and then
press “Zero" button while holding him.
2. Pressing "Zero” button also causes scale to find its zero
reference point to assure accurate measurements. When
"Zero” button is pressed, moving dashes will appear on
the display for a few moments. Wait until the dashes stop
and a “0” appears before touching the scale.
3. “ Lock-Average" Button—Locks the average weight
computed by the microprocessor during the last 4
seconds, on the display. Press button again to unlock
display. Leave button “locked” to retain last weight
measurement if desired.
5. Minimum Displayed Weight—Scale will not display a
weight of less than 15 grams.
6. “Read Light’!—Comes on when “Lock Average" button is
pressed, to indicate that weight is locked on display.
7. “Overload” Light—Will flash if weight on scale exceeds
maximum capacity of 10,000 grams (22 pounds).
8. Dashes—Flash for few seconds during warm-up when
scale is connected to power. Dashes also appear
momentarily after “Zero” button is pressed.
9. “Cable”—Appears as reminder if cable between
Display/Control Unit and weighing platform has not been
connected.
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Pago 4-1

Warm-Up
The scale is always on when it is connected to an eiectrical
outlet. When first connected to an electrical outlet, a series of
dashes will flash for a few seconds on the display to indicate
the scaie is warming up. When dashes have been replaced by
numbers, the scale is ready for use.
To Cancel Weight of Bedding—
After the bed is made OR whenever the bed linen is changed,
foilow these steps;
• Press “Display On/Off” button to tu(fl on display.
• If display is locked (“Read" light on), press "Lock" button
to unlock.
• After changing bed linen, make sure that the bedding is
touching only the mattress and scale platform (fig. 4-2).
• Make sure there are no extra objects on the scale (teddy
bears, etc.).
• Before placing baby on scale, press “Zero" button. This
cancels all weight on scale. The display will momentarily
show a series of moving dashes. Do not touch the scale
until a “0" appears on the display. (If baby is already on
scale, lift him off platform and press “Zero" while holding
him.)
1
To Weigh Baby
• Press “Display On/Off" button to turn on display.
• If display is locked (“Read" light on), press “Lock" button
to unlock.
• Remove all loose objects from mattress and scale platform
(teddy bears, scissors, etc.)
• Press "Gms/Lbs" button to select weight units.
• Lift IV tubes, monitors, leads, etc., and hold as steady as
possible. (See next page for suggestions on lifting
technique.)
• Take weight measurement—using either of following
methods:
1. Mental Average— Watch weight on display a few
seconds, then select your best “mental average"
weight. If you desire to verify the weight, take second
"average!' Then lay tubes and leads down and chart
weight.
2. Use “Lock-Average" Button— While you are holding
the tubas and leads, have another nurse push the
"LocknAverage" button. The best average weight,
computed by the microprocessor during the last 4
seconds, will be locked on the display. Lay tubes and
leads down and then chart weight. '
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• Place baby in center of scale mattress.
• Proceed with weighing. (See next section.)
NOTE: Negative Weight If negative weight numbers appear
on the display (example: -150 gms) it indicates that some
weight has been removed from the platform after the “Zero"
button was pressed. Before placing baby on scale, press
“Zero” and display will return to “0!'
NOTE: Minimum Displayed Weight. Scale will not display a
weight of less than 15 grams.
Display On/Off
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Display can be turned off between weighings, if desired, by
pressing "Display On/Off’ button. The scale remains on even
when the display is off, so it does not require a further warm¬
up period.
Memory Feature
Smart Scale has a memory that retains all previous data when
the display is turned off or even if electrical power is
disconnnected. If the weight of the bed linen was previously
cancelled out (by the “Zero" button). It will remain cancelled
when the display is turned on again, and weighing can be
resumed.
To Retain Last Weight Reading
The last weight reading can be locked on the display by
pressing the “Lock-Average” button. This weight will be
retained as long as the display is locked and even while the
display is turned off.
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Cieaning
Smart Scale can be wiped with a cloth dampened with any
ordinary hospital disinfectant. Be careful not to spill any liquid
on the scale that might enter the case and damage the
electronics.
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Page 4-2
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Lifting IV Tubes and Monitor Leads
Make sure
tubes are not
touching platform
Fig. 4-3
For the most accurate, repeatable weight measurement when
holding up IV tubes and monitor leads, follow this technique:
1. Before lifting the tubes and leads, note the total weight
displayed on the scale. Usually, lifting the tubes and leads
will reduce this weight from 25 to 50 grams.
2. Pick up the tubes and leads approximately 10" from where
they are attached to the baby.
3. Do not hold the tubes and leads tightly. Let them rest in the
open palms of your hands while lifting.
4. Gently raise your hands to the point where the tubes and
leads are just lifted off the baby’s body—but no higher.
Lifting higher than is necessary can cause greater
deviations in weight measurement.
5. Before faking weight reading, make sure that no tubes or
leads are accidentally touching the scale platform.
VENTILATOR VIBRATION ON RADIANT WAR¬
MER BED WHILE ZEROING SCALE
When using ventilator on baby, prior to pushing zero, ventilator
tubes should be lifted clear (Fig. 4-4) and not allowed to touch
any part of radiant warmer. Once zero appears on readout,
ventilator tubes may be returned to normal position.
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Page 4-3A

Sect/on Five
Service.
OLYMPIC SMART SCALE MODEL 35
Calibration
As with any precision electronic instrument, the Smart Scale
can drift out of calibration over time. Since no electronic scale
recalibrates itself automatically, the only vray to assure correct
recalibration is to place an accurate, known weight on the
scale and make the required internal adjustments so that the
scale displays the correct weight.
Calibration Weight
The Smart Scale calibration procedure requires a weight of
5000 ± 1 gm. If not available locally, this calibration weight
may be ordered from Olympic Medical Corp. (Cat. No. 56332).
Calibration Upon Receipt
The Smart Scale was calibrated at our factory in Seattle prior
to shipment. However, it should be recalibrated before being
put into service because local variations in the force of gravity
can affect calibration as much as 20 grams.
1. Remove the calibration cover on the readout unit (fig. 5-1)
to expose the calibration controls. Unplug the power cord.
2. Set the DIP switches as follows (fig. 5-2);
S1-1 Off (down)
S1-2 On (Up)
Si-3 Off (down)
Si-4 Off (down)
3. Turn the fine caiibration pontentiometers (R7, R21) to their
mid-range.
4. Exercise the weighing platform load cell by placing the 5 kg
calibration weight in the center for 10 seconds, then
remove the weight for 10 seconds. Repeat 10 times.
5. Connect the power cord to electric power. Scale display will
show “SCALE” then "CALIb” to indicate the calibration
mode.
CAUTION
Do NOT press the ZERO button
Calibration Frequency
Smart Scaie calibration should be checked every six months
for the first year. Then the frequency can be adjusted based on
how far the Smart Scale has drifted. If it is staying within 1 or 2
grams, the calibration frequency can be reduced to every 12
months. Pdr larger weight drift, increase the calibration
frequency. If the drift is very large, check the Troubleshooting
Section.
7. Place the 5.0 kg calibration weight in the center of the
weighing platform. Allow the display to stabilize for 10
seconds.
8. Adjust R2 (COARSE ZERO) so that the display reads
32,768 ± 30.
9. Adjust R7 (FINE ZERO) so that the display reads
32,768 ± 4.
Calibration Procedure
Make sure the vwighing platform is on a firm, level surface.
The platform must be connected to the readout unit. Attach the
extension platform (with mattresses in place). For best results,
ambient air temperature should be between 70° - 75°F (21.2° -
23.90C).
NOTE: Due to electronic system "noise,” the display will
jitter ± 4 counts around this value. This is normal.
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Page 5-1

10. P ress the ZERO button. Display will read 0 ± 4.
11. Remove the calibration weight. Allow 10 seconds for
display to stabilize.
12. Adjust R18 (COARSE SPAN) until the display reads
-20,000 ± 30.
14. Press ZERO. Display should read 12,768 ±4. If not, repeat
steps 7 thru 13 omitting the coarse adjustments of steps 8
and 12.
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15. Put all DIP switches in the Off (down) position and replace
the calibration cover.
13. Adjust R21 (FINE SPAN) until the display reads
-20,000 ± 4.
NOTE: Due to electronic system "noise," the display will
jitter ± 4 around this valua This is normal.
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Troubleshooting
The Olympic Smart Scale is designed to allow field servicing
down to the printed circuit board (PCB) level. These
instructions will assist you in isolating the problem PCB or
component. The faulty board must be returned to Olympic
Medical for repair or replacement.
In order to identify the problem, please read the
"Troubleshooting” and the “Theory of Operation” sections
carefully.
Static and Contamination: The integrated circuits and
semiconductors on the PCBs can be damaged by electrostatic
discharge or contamination by body oil. Observe proper
handling precautions at all times.
Service requires disassembly of the Display/Control Unit be
performed by qualified personnel only. Do not remove printed
circuit boards for troubleshooting.
NOTE: The weighing platform is not a field repairable item and
should not be disassembled. If the weighing platform is
suspected of being defective it should be returned to Olympic
Medical. When the platform is replaced or repaired the scale
should be recalibrated.
Troubleshooting Hints
• Perform a visual inspection. All connectors and cables
should be connected and secure. Check for chafed or
pinched wires. Check for signs of components overheating.
Check that alt socketed parts are firmly seated in their
sockets.
• Analyze symptoms BEFORE disassembly and
troubleshooting. Read the theory of operation so you
understand the system. Formulate a theory of a possible
cause for the symptom and make tests to check your
theory.
• Check the easiest and obvious first (such as fuses,
mechanical interference, etc.).
• Make measurements with respect to signal ground, TP4 on
the Digital board.
Static and Contamination Awareness
Most integrated circuits and semiconductors in this Scale can
be damaged by electrostatic discharge. Exercise proper
handling precautions to avoid damage.
• Minimize handling.
• Discharge your own static by touching grounded metal or
by wearing a grounded wrist strap, before touching parts.
• Keep replacement boards in their anti-static bags until
ready to use.
• Avoid touching pins or traces. Handle PCBs by edges to
avoid static discharge and avoid contamination by oil from
fingers.
• Avoid plastic, vinyl and styrofoam in the work area. Avoid
wearing clothing which may pick up static electricity.
• Do not slide PCBs or components over any surface.
Disassembly for Troubleshooting
CAUTION
Disconnect power cord from wall outlet.
1. Disconnect weighing platform connector at back of readout
unit.
2. Remove the calibration cover at the front of the readout
(fig. 5-3).
3. Remove the large screw in the center of the readout (under
the calibration cover).
4. Pivot bottom of enclosure. Lift tab (in front half) out of slot
(fig. 5-4).
5. Separate enclosure half to allow access to green ground
wire. Disconnect wire (fig. 5-5).
6. Unplug P8 from J8 at the back of the display board
(mounted in the front enclosure) and unscrew the green
ground wire lug on the front of the chassis. The front half¬
shell can now be removed exposing the chassis. Digital
board and Analog board are mounted in the rear
enclosure.
7. The Display board and front panel assembly can now be
removed from the front enclosure if desired.
8. To remove the chassis holding the other PCBs, lay down
the unit on a soft surface.
9. Unscrew the four recessed screws in the rear.
to. Unscrew the 2 clamp studs, disassemble clamp, spring,
washer.
Front Enclosure
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Rg. 5-3
Page S-3A

11. Gently pull out the chassis assembly and slide the rear
piastic case back a few inches on the power cord (fig. 5-4).
12. Reconnect display cable (P8) and green grounding wire to
chassis. Ali test points are now exposed and unit is ready
for troubieshooting.
13. Connect weighing platform cable to Display/Control Unit.
Then connect power cord to wall outlet.
When unit is plugged in to 115 Vac, there is
danger of electric shock anywhere up to the transformer. Use
extreme care.
Proceed to next page for Troubieshooting.
Reassembly After Troubleshooting
1. Make sure eiectric power cord is disconnected from outlet.
2. Slide the chassis assembly into place.
3. Reattach the four reccessed screws in the rear.
4. Reassemble clamp, adjust spacing .80" away from
enclosure.
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7. Tighten the central screw.
8. Replace the calibration cover.
Removing Analog/Digital PCBs
w;ViH*)fi Make sure electric power is disconnected from
wail outlet. Do not remove PCBs for troubleshooting.
First, disassemble per steps 1 through 10 in Disassembly
instructions.
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1. D isconnect PI from the transformer (on the rear chassis) to
J1 on the digital board.
2. Disconnect P5 from J5 on the anaiog board (fig. 5-5).
3. Remove the PCB assembly by removing the four screws
and kep nuts on the digital board angle brackets.
4. Separate the two PCBs by unscrewing the screws in the
four standoffs holding them together (fig. 5-6).
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Reassemble the boards to the chassis by reversing the above
steps.
5. Make sure the display cable and ground wire are
connected.
6. Replace the front half of the enclosure.
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Symptoms and Suggested Tests
Scale will not zero with the “Zero” button:
CHECK IF DISPLAY SHOWS "WALKING” DASHES AFTER
“ZERO” BUTTON IS PRESSED. If it does but the unit will not
arrive at a steady zero, there are tvro possible causes:
1. THE SIGNAL IS BEYOND THE ZERO CAPTURE RANGE.
2. THE SIGNAL IS TOO UNSTABLE TO ACQUIRE ZERO.
Both could be caused by a power problem. Check +5V
DIG, +5V ANA and -5V ANA at test points. (Gnd is TP4,
+5V DIG is TPS on Digital Board, +5V ANA is TP4, -5
ANA is TPS on Analog Board.) If voltages are OK, check
signals on Analog board. Make sure load cell connector is
plugged Into J5. The analog signal at TP2 must be between
+1.010 V and -1.010 V to be within the A/D range. Typical
signal at TP2 with no load (if zero pot is adjusted properly)
is -0.670 V. The typical reference voltage on the A/D at
TPS is 0.549 V.
IF NO “WALKING" D/fiHES APPEAR WHEN “ZERO”
BUTTON IS PRESSED:
1. Make sure scale is “unlocked” (Green READ LED off).
2. Check cables and connectors from front panel to digital
board. Pressing the “Zero” button should cause a low on
RN1, Pin S and/or on U6, Pin 1.
Scale won’t come on when plugged In to power:
1. Check fuse. Make sure connector PI from the transformer
is connected to J1 on the Digital board.
2. Check that CR9 LED on Digital board turns on. If so, and if
+5V DIG is present at TPS, check that this +5V and
ground is getting to the microprocessor.
S. If CR9 won’t illuminate, check that +8V is present at TP2
on the Digital board.
4. If +8V not at TP2, check the ac input through FI and filter
FLI to primary of T1. T1 secondary voltage coming into J1
(pins 1 and S) should be about 1S.5 Vac (no load). If not, the
transformer, T1, is defective.
5. Voltage across the large electrolytic capacitor C2 should
be about 15 Vdc. If not, check bridge rectifier diodes,
CRI - CR4 and transient suppressor CR5. If OK, replace
the digital board.
6. If voltage is present across C2 but yet no +8V at TP2,
regulator VR1 is bad; replace Digital board.
Scale will not “lock” the display and the READ light
will not come on:
1. Check that the DIP switch Si-4 on Analog board is off
(down).
2. Pressing LOCK/AVG should provide a low to pin 16 of U6
on Digital board. If not, check membrane switch on front
panel and connectors down to the Digital board.
3. If pin 16 of U6 Is getting the signal but the lock function is
still inoperative, replace Digital board.
Scale will not change units:
1. Pressing the GM/LB switch should provide a low to pin 23
of U6 on Digital board.
2. If not, check membrane switch on front panel and
connectors down to the Digital board. If pin 23 of U6 is
getting the signal, replace Digital board.
Some segments or annunciator lights do not come
on:
1. Turn on the scale by plugging it in while holding any one of
the front panel switches. This will allow viewing of ail
segments and lights.
2. If all LEDs do not light, replace the display board.
Scale will not weigh accurately:
1. Verify calibration.
2. Check that nothing (cables, etc.) is touching or rubbing on
the platform. All load must go through the load ceils.
3. If there is hysteresis exceeding ±2 grams (it vreighs
differently going up in weight than going down in weight),
send platform to Olympic Medical for service.
4. Slight linearity errors (exceeding specifications) or off-
center load errors are probably due to a defective load cell.
Replace weighing platform.
5. If errors are random or there is a linearity problem, check
power supply voltages.
6. If power supply voltages are OK and getting to the Analog
board, weighing inaccuracy or drift can be caused by the
load cell or the Analog board.
7. Using a digital voltmeter of adequate resolution (4V2 digits
or better) and sensitivity, with ungrounded (floating)
differential input, monitor the load cell output directly
betwreen pins 5 of U1 and U2 on the Analog board.
8. The +5V analog used for load cell excitation should also
be monitored and load cell signals normalized to that. This
could determine if load cell or the Analog board is the
cause. If not sure send both the platform and the Analog
board back to Olympic Medical for analysis.
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Page 5-5

Theory of Operation
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Refer to fig. 5-8 for a block diagram.
Load Cells
Two load cells in the weighing platform each form a
Wheatstone Bridge and are connected in parallel (fig. 5-7). An
excitation voltage is applied at two opposite corners and a
signal voltage comes off the remaining two corners. As weight
is applied, two “resistors" are in compression and two are in
tension, changing the resistance and causing a differential
analog signal voltage which is proportional to the applied
weight.
Analog Board
Signal Flow: The load cell analog signal is amplified by an
instrumentation amplifier. Then it is filtered and sent to the
Analog-to-Digital converter which provides binary data to the
microcomputer (on the digital board).
The analog board also holds the DIP switches used in the
calibration procedure.
Circuit Description: U1 and U2 form a differential, chopper-
stabilized instrumentation amplifier. The gain of U1 and U2 is
fixed by RIO, R11, and R14 at 187.2. These are special,
precision-matched resistors. Amplifier input is guarded at the
common mode voltage of approximately +2J5 volts, provided
by ua U4, a high-accuracy unity-gain amplifier, changes the
differential input to a single-ended output. Zero offset is
provided by R2, R7, and U9. The signal from U4 output is fed
through either fitter 1 or 2 to the input of the A/D converter.
Analog switches in U7 are used to seiect the appropriate filter.
Filter 1: A “light" fitter that allows rapid acquisition of the
weight data. This filter is used during weighing. The
microcomputer provides averaging to get the best possible
approximation of weight. The average of the last 35 seconds of
readings is displayed when scale is locked.
Filter 2: Smooths out signal while scale is zeroing. The filter is
automatically selected by the microcomputer.
Analog to Digital (A/D) Converter
U8 is an integrating dual slope-type converter with a
conversion cycle of approximately 400 milliseconds. The
dynamic range is ±32,768 counts (15 bits pius sign, or a totai
of 65536 counts). The input signal to the A/D converter is 134
microvolts per gram.
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The converter internally resolves to Va gram. It divides 10
kilograms (maximum weight for scale) into 40,000 counts
(±20,000 range). A/D gain is controiied by R18 and R21, whicf||
provide a reference voitage that is Vi of the A/D range, or 054*
volts (typically) at TP3.
The A/D gain is fuily ratiometric. If the ±5 volt excitation signa|||
to the load cell decreases slightly, the load cell output signal *
decreases proportionately. The A/D reference voltage will also
decrease, thus increasing the A/D sensitivity (gain) and the ^
resultant digital output will remain the same. ■
Zero offset is such that 5.0 kg provides a zero input voitage to
the A/D converter. 10 kg will equal -1-0.67 volts and 0 kg equalsB
-0.67 volts (measured at TP2). |||
Zero offset voltage at TPl will be lower than -0.67 volts
because it must also cancel out any load cell zero offset and |||1
the weight of the mattress, supporting structure, and the ■ -!
extension platform with its mattress. Voltage at TPl will
typcially be around -1.23 volts if there is no load cell offset
and the extension platform is in place.
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The microcomputer (next section) monitors the DATA VALID
line. When it is “valid,” the microcomputer reads the A/D
binary output. Depending on the request by the
microcomputer, via the high byte or low byte enable lines, the
A/D converter presents the high order or low order bits on the
eight data lines. ||||
NOTE: All voltages are nominal. Each scale varies depending
on its specific load cell sensitivity and zero offset.
Digital Board
signal Flow: The A/D signal is processed by the micro¬
computer which has an input-output (I/O) expander. The
microcomputer has internal RAM (random access memory).
An external EPROM, U5, (erasable-programmable read only
memory) is used.
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Circuit Description: The microcomptuer, U3, is an 80C39. It
has 128 bytes of internal RAM. Microcomputer operation is
controlled by software in the EPROM. An external, non-volatila^^
RAM, U7, is used to store zero reference and mode data while
scale is disconnected. The computer performs the foliowing
duties:
1. Housekeeping Chores. Such as initialization. Checking
for overrange, and checking if the platform cable is
connected.
2. Zero Tracking. If zero shifts of less than ±3.25g occur.
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3. Computes Correct Weight. Determines weight in grams
and pounds/ounces when weight is applied. Suppresses
readings below ± 15 grams.
4. Selects Analog Filter. Light filter for weighing; heavy filter
for zeroing.
5. Averaging Routine. Locks the average of the last 8
readings on the display.
6. Continuously scans the front panel switches. Changes
units, zeros, locks or unlocks and turns the display on or off
as requested.
7. Display signal decoding or other formatting to illuminate
the correct digital segments and annunciator lights.
8. Updates the non-volatile memory whenever the units,
mode or zero reference is changed.
The Input-Output (I/O) Expander: Receives data signals from
the microcomputer and the switches on the front panel. It also
controls the display drivers for the front panel and transmits
serial data to each one. It also communicates with the non¬
volatile RAM.
Display Board
Data is simultaneously clocked into two display drivers via a
common clock. The format is one start bit followed by 35 data
bits. On the 36th clock cycle, all 35 data bits are latched to the
outputs of the display drivers.
Each dispiay driver has a brightness control (R3 and R8). By
placing an ammeter between appropriate terminals of El, it is
possible to measure current of a group of lit segments.
Power Supply
Power supply for the Smart Scale Model 35 is divided between
the two major printed circuit boards and the chassis.
Chassis Mounted Components: AC power from the power
cord comes into the chassis of the Display/Control unit. The
chassis has F1 (a normal blow fuse), a filter, and a transformer.
The secondary of the transformer is connected to the digital
board through P1-J1.
Digital Board Components: CRI through CR4 form a full
wave bridge rectifier. CR5 is a transient voltage suppressor,
and C2 and C3 provide filtering. VR1 is a +8 volt voltage
regulator. All scale current goes through VR1. All these circuits
are live when the scale is plugged in, whether the display is on
or off.
Circuit Description: Voltage regulator VR2 provides a digital
-1-5 volts. CR9, a small LED, situated on the digital board is on
when the scale is plugged in.
Analog Boad Components: Power comes off the digital board
and goes to U5, a negative switching regulator, and VR3, a -i-5
volt voltage regulator. U5 provides a negative voltage. VR3
provides a regulated -1-5 volts for the analog circuitry. The
negative voltage from U5 is applied to U6, which has a gain of
-1. U6 inverts the +5 volt analog from VR3 to a tracking -5
volt analog voltage. The A/D is on the analog board. See
section A/D.
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Fig. 5-8
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