Data acquisition system

A data acquisition system utilizing a microcomputer and incorporating a plurality of monitors each adapted to produce an electrical signal indicative of a physical condition of apparatus to be monitored. The electrical signals are fed via multiplexing equipment and analog-to-digital converters into the microcomputer which is equipped with print-out means. The system is such that the level of any one or all of the signals from the respective monitors can be printed out as well as a change in the condition of any signal. Means are incorporated into the computer for calculating and printing the trend (i.e., the slope of a plot of signal amplitude versus time) of a succession of stored signals from any monitor which would indicate a probable malfunction of a device being monitored and the probable time to failure. In the case where the signals from the monitors comprise vibration signals, the system performs an automatic frequency spectrum analysis whenever a probable or actual malfunction is detected.

While not limited thereto, the present invention is particularly adapted 
for use in monitoring vibrations produced by rotating or other types of 
machinery in a complete industrial installation, such as a refinery. By 
monitoring vibrations in this manner, malfunctions and probable future 
failures of any machines within the industrial installation can be readily 
ascertained; and corrective action can be taken immediately and before a 
breakdown or possible dangerous condition occurs. 
There are at present essentially two types of data acquisition systems--the 
dedicated minicomputer system and the simple data logger. Computer systems 
generally include disc memory for data storage, CRT terminals for display 
of data and line printers for hard copy of data. As a result, they require 
a relatively large capital investment. While simple data loggers are 
relatively inexpensive, they offer simple functions only such as logging 
data and comparing the data to setpoints. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a data acquisition system is 
provided which does not require a large capital investment but which, 
nevertheless, is capable of printing out complete system information 
including a malfunction of any one of a number of different devices being 
monitored, the time to failure of any piece of equipment being monitored, 
and an analysis of the input information. In the case where the invention 
is used in a vibration monitoring system, it performs the functions of 
automatic channel data logging, frequency spectrum analysis, and vibration 
level trend prediction. Each of these functions additionally may be 
manually selected for each individual monitor or channel via front panel 
controls. A built-in system fault detection circuit is used which will 
respond to either an internal or circuit fault or to an external system 
alarm relay closure. Data readout is obtained via a self-contained 
dot-matrix printer assembly. 
All functions of the data acquisition system of the invention are under the 
control of an internal microcomputer which continuously samples data from 
a plurality of monitors. At each monitor, vibration input signals are 
obtained directly from velocity pickups, self-amplified accelerometers, 
noncontact signal sensors or from accelerometer preamps. In addition, 
direct current signals proportional to vibration level or amplitude and 
trip alarm signals are obtained from the monitors, these latter signals 
being derived by comparision of the actual vibration signal with reference 
signals proportional to preselected alarm and trip levels. 
The system automatically indicates, via the computer print-out, those 
channels which go into a trip condition within a preselected time span. 
That is, the time to failure is calculated and displayed via the 
print-out. Each channel's "look ahead" time may be selected with a 
user-programmable jumper board within the computer. Additionally, trend 
prediction for any individual channel or monitor may be manually requested 
at any time via front panel trend and channel selection switches. 
The system also incorporates frequency spectrum analysis circuitry which 
provides frequency spectrum sampling of input vibration signals over a 
wide range of frequencies in 1/20 octave steps. Only those frequencies 
whose amplitudes are greater than 10% of full scale are listed on the 
paper tape computer print-out, along with the overall vibration level. 
Vibration analysis is performed automatically upon receipt of a trip or 
alarm signal, for a calculated trend alarm for any channel, or at preset 
intervals. The paper tape print-out indicates which channel has gone into 
a fault condition and what that condition was (i.e., trip, alarm or trend 
alarm) as well as a change in any channel's condition.

With reference now to the drawings, and particularly to FIG. 1, the data 
acquisition system shown includes forty-eight channels or monitors for 
monitoring a physical condition of a device to be monitored. Only monitor 
Nos. 1 and 48 are shown in the drawing and are identified by the reference 
numerals 10 and 12. It will be further assumed for purposes of explanation 
that the data acquisition system is to be used in a vibration monitoring 
system. Thus, each monitor, such as monitor 10, is connected to a 
vibration pickup 14 in contact with a bearing of a rotating member 16, for 
example, and adapted to produce either a displacement, velocity or 
acceleration vibration signal. Pickup 14 is connected through an amplifier 
18 to a rectifier 20 which will produce an essentially steady-state direct 
current output signal on lead 22-1 which is applied to one input of a 
first multiplexer 24. Similarly, each of the other monitors will apply an 
input to the multiplexer 24, only the lead for the last monitor 48 being 
shown in the drawing and identified by the reference numeral 22-48. 
The oscillatory vibration signal from the pickup 14 is also applied 
directly via lead 26-1 to a second multiplexer 28. The same is true of the 
remaining monitors, the oscillatory signal for the last monitor 12 being 
applied via lead 26-48 to multiplexer 28. Each of the monitors also 
incorporates first and second comparators and relays 30 and 32. In 
comparator 30, for example, the direct current signal from rectifier 20, 
representing the amplitude of the vibration signal, is compared with a 
direct current signal from D.C. reference voltage source 34. If the direct 
current signal from rectifier 20 equals or exceeds the magnitude of the 
signal from source 34, then a relay is actuated to produce a steady-state 
direct current signal on lead 36-1 connected to the input of a third 
multiplexer 38. The amplitude of the direct current signal from rectifier 
20 at which the relay is closed to energize lead 36-1 is chosen 
arbitrarily and represents that amplitude of the vibration signal which 
signifies an alarm condition (i.e., an imminent malfunction). Similarly, 
the output of rectifier 20 is compared with a direct current signal from 
D.C. reference voltage source 40 in the comparator and relay 32, the 
arrangement being such that when the amplitude of the vibration signal 
reaches a point where the device being monitored should be shut down, the 
relay is actuated to energize lead 42-1. This trip signal on lead 42-1 is 
also applied to the third multiplexer 38. Even though the equipment in 
question may be shut down automatically upon receipt of a trip signal, 
ordinarily sufficient momentum of the rotating parts, for example, will 
keep the parts rotating for a sufficient period of time to permit a 
meaningful spectrum analysis and data log to be taken. Alarm and trip 
signals are also applied to the multiplexer 38 from each of the other 
forty-seven monitors, the alarm signal from monitor 12 being on lead 36-48 
and the trip signal from monitor 12 being on lead 42-48. 
Included in each monitor, such as monitor 10, is an external fault detector 
44 adapted to detect faults such as a change in impedance due to breakage 
in the cable leading to the pickup 14 or an inaccurate gap for a 
non-contact vibration pickup such as that shown in U.S. Pat. No. 
3,707,671. Whenever an external fault occurs, a signal is applied to the 
trip lead 42-49, common to all monitors, and applied to the multiplexer 
38. As will be seen, in the particular embodiment of the invention shown 
herein, the occurrence of an external fault at any monitor causes a 
printer to print-out "SYSTEM ALARM" without identifying the channel from 
which the fault signal was derived. This must be derived by manual 
examination of each monitor. 
A manual programmer 46, comprising an internal jumper board, allows manual 
selection of individual channel parameters such as trip level setpoint for 
trend prediction and full-scale range for each channel, along with 
appropriate units of measure such as mils, inches per second or G's. A 
selection of sixteen combinations of (i.e., four binary bits) full-scale 
range in engineering units is provided for each channel. These sixteen 
choices, specified by the user of the data acquisition system, are coded 
into the custom-programmed module or programmer 46 which forms part of the 
internal computer memory. The jumper board allows individual channel 
selection to any one of sixteen choices. In addition, functions common to 
all forty-eight channels may be selected on the jumper board 46, such as 
repetition rate of automatic data log print-out and "time until trip" 
setpoint of a trend alarm. Each of the inputs from the programmer 46 
passes through a digital multiplexer 48 to a computer 50 along with the 
inputs from multiplexers 38 and 24. 
The multiplexer 48 is controlled from the computer 50 by means of a 
nine-bit address input 52. Similarly, multiplexer 38 is controlled so as 
to select a particular input channel monitor via a seven-bit address input 
54. Multiplexer 24 is controlled by a six-bit address input 56; however 
the output of the multiplexer 24 must pass through an analog-to-digital 
converter 58 before being fed into the digital computer 50 since the 
signals on leads 22-1 through 22-48 are direct current signals whose 
magnitudes are proportional to the magnitudes of the vibration signals 
being monitored. The multiplexer 28, to which the oscillatory vibration 
signals on leads 26-1 through 26-48 are applied, is also controlled by a 
six-bit address input 60. A strobe input is applied to each of the 
multiplexers 24 and 28 via leads 62; while an end of conversion signal 
from each of the analog-to-digital converters 58 and 84 is fed back into 
the computer via leads 64. 
The oscillatory vibration signals at the output of the multiplexer 28 are 
applied to the novel spectrum analyzing apparatus of the invention, 
enclosed by broken lines in FIG. 1 and identified generally by the 
reference numeral 66. It comprises a single-double integrator 68 
controlled by a signal from the computer 50. It is desired to perform a 
spectrum analysis on a vibration displacement signal. Hence, if the signal 
detected by any monitor is not a displacement signal but rather a velocity 
signal, a single integration is performed to convert it to a displacement 
signal. On the other hand, if the signal produced by a monitor is an 
acceleration signal, a double integration is performed to convert the 
acceleration signal to a displacement signal. 
From the sixteen combinations selected by the manual programmer 46, it is 
known whether or not integration is required and the gain required for 
amplifier 70. For example, if channel No. 21 is programmed in mils (i.e., 
displacement), a single integration is required to convert a velocity 
signal in inches per second to mils. Additionally, the gain of amplifier 
70 is adjusted to give a full-scale output for the particular vibration 
pickup used. For example, if a velocity pickup for channel No. 10 has an 
output of 764 millivolts RMS per inch per second peak, then the amplifier 
gain must be ten to achieve a 7.64 volt full scale output required for a 
peak detector 80 adapted to detect a peak voltage of 10 volts, as dictated 
by an analog-to-digital converter 84. 
The output of the integrator 68 is coupled through the programmable gain 
amplifier 70 to the input of a voltage tuned filter 72 which has a 
passband which sweeps through the expected range of frequency components 
of an incoming vibration signal. The operation of the voltage tuned filter 
is schematically illustrated in FIGS. 4 and 5. The passband of the filter, 
indicated by the reference numeral 74 in FIG. 4 is caused to sweep through 
a frequency range of 600 cycles per minute to 600,000 cycles per minute. 
This sweep takes a total of twenty-four seconds. However, in order to 
obtain a good frequency sample, it is necessary to have the passband dwell 
at each frequency being sampled for at least 2 cycles of the selected 
frequency. The dwell times are shown in FIG. 5 and it will be noted that 
the dwell time for each frequency is 2 divided by the selected frequency. 
Thus, at the lowest frequency of 600 cycles per minute (10 cps), the dwell 
time is about 1/5 of a second. The dwell time for each successive step 
decreases until, at a frequency of 6000 cycles per minute, for example, it 
is 1/50th of a second. The time to sweep through the band of frequencies 
from 600 to 6000 cycles per minute, as shown in FIG. 4, is about eighteen 
seconds; however the time required to sweep through the band between 6000 
and 60,000 cycles per minute is only four seconds; and the time to sweep 
through 60,000 cycles per minute to 600,000 cycles per minute is only 
about two seconds. 
The manner in which the passband sweeps through the spectrum is controlled 
via address inputs or bits on lead 76 from the computer 50 applied to the 
voltage tuned filter 72 through a digital-to-analog converter 78. Signals 
passing through the voltage tuned filter are applied to the peak detector 
80, the arrangement being such that only those frequencies whose 
amplitudes are greater than 10% of the full-scale value as determined by 
the internal computer program will be listed in the computer print-out. 
The peak detector 80 is reset by signal on lead 82 from the computer prior 
to each frequency sample derived from the voltage tuned filter 72. From 
the peak detector 80, the signal passes through the analog-to-digital 
converter 84 to the computer 50. The computer 50 includes the usual 
input-output interface 86 connected to a central processing unit 88, the 
central processing unit 88 being controlled by a read-only memory 
comprising the computer program 90 and a random access memory 92. The 
input-output interface is also connected to a printer 94. 
In addition to automatic functions, it is also possible to manually obtain 
data from any monitor or channel by means of touch switches 96 and 98. In 
the illustration given in FIG. 1, for example, the switches 96 and 98 have 
been adjusted to receive information from channel 17. After the channel is 
selected, a system test can be achieved by depressing touch switch 100. 
Similarly, a data log can be achieved by depressing touch switch 102 and a 
spectrum analysis can be achieved by depressing switch 104. Finally, a 
trend analysis can be achieved from any monitor by depressing touch switch 
106, these switches being connected through a touch switch interface 108 
to the computer 50. When touch switch 100 is depressed, a test voltage 
source 110, for example, will apply test voltages to two selected 
channels. 
A flow diagram of the computer program utilized with the invention is as 
follows: 
______________________________________ 
DECLARE ALL VOLTAGES 
TO BE READ INTO STORAGE 
.dwnarw. 
CONSTRUCT TABLE OF 
FREQUENCIES TO BE 
PRINTED OUT (Read-only memory) 
.dwnarw. 
CONSTRUCT TABLE OF 
TUNING VOLTAGES FOR 
VOLTAGE TUNED FILTER 
67 tenth-octave filters (Read-only memory) 
.dwnarw. 
ACTIVATE DC 
MULTIPLEXING (MULTIPLEXER 24) 
.dwnarw. 
READ INTERNAL 
CLOCK - HOURS 
& CALCULATE DAYS through 365 
.dwnarw. 
SELECT CHANNEL #FOR MANUAL 
ANALYSIS AND TREND 
.dwnarw. 
TEST ALARM STATUS 
.dwnarw. 
ACTIVATE DIGITAL 
MULTIPLEXERS 38 and 48 
.dwnarw. 
ACTIVATE STATUS FILE 
.dwnarw. 
ESTABLISH TREND 
ALARM (same time for all channels) 
.dwnarw. 
READ IN FULL SCALE 
& ENGINEERING UNITS 
.dwnarw. 
ESTABLISH DATA LOG 
SCHEDULE PRINT-OUT 
.dwnarw. 
ESTABLISH AUTO DATA 
LOG PRINT-OUT 
ESTABLISH AUTO 
ANALYSIS PRINT-OUT 
.dwnarw. 
SCALING FACTOR FOR 
FULL SCALE 
MANUAL DATA LOG 
INPUT COMMAND 
.dwnarw. 
MANUAL TREND 
.dwnarw. 
MANUAL ANALYSIS 
.dwnarw. 
CALCULATE TREND 
FOR ALL CHANNELS 
& STORAGE WITH last 
5 Hourly Readings 
.dwnarw. 
COME WITH 
ESTABLISHED TREND 
ALARM 
.dwnarw. 
ANALYSIS PRINT-OUT 
.dwnarw. 
DATA LOG PRINT-OUT 
.dwnarw. 
TREND ALARM PRINT-OUT 
.dwnarw. 
SYSTEM ALARM PRINT-OUT 
______________________________________ 
The first step in the program is to declare all variables to be read into 
the random access memory 92 and their location in storage. This includes 
direct current amplitude signals from multiplexer 24, the signals from 
manual programmer 46, and the trip and alarm signals from multiplexer 38. 
A table of frequencies to be printed out in each spectrum analysis is then 
constructed from data permanently stored in the read-only memory 90. This 
table is the same for all channels; however only those frequencies will be 
printed out which exceed 10% of full scale in amplitude. The next step in 
the program is to construct a table of tuning voltages derived from the 
read-only memory 90 for the voltage tuned filter 72, this corresponding to 
the table of frequencies to be printed out. Direct current multiplexing by 
multiplexer 24 is then activated; whereupon each of the direct current 
amplitude signals from the multiplexer 24 is sampled in succession. This 
is followed by a reading of the internal clock in hours and days, the days 
being calculated from accumulated hours. The internal clock is capable of 
indicating the day of the year from 1 through 365 as well as time of day 
up to 24 hours. 
The following step in the program is to select a channel for manual 
frequency analysis or trend analysis. In this phase, the central 
processing unit 88, activated by touch switches 96 and 98, is conditioned 
to receive signals from a single channel to perform a spectrum analysis 
upon depression of touch switch 104 or a trend print-out upon depression 
of touch switch 106. Thereafter, a test alarm status is performed by 
momentarily altering internal test voltages. The print-out will indicate 
system alarm and system normal as test voltages are altered, then returned 
to normal. This step insures that the internal computer circuitry is 
operating properly. The digital multiplexers 38 and 48 are then activated 
to read-in alarm and trip signals as well as information from the manual 
programmer 46. A status file is then activated to store normal, alarm and 
trip signals and to determine whether there has been a change in an alarm, 
trip or normal signal. Following this, the trend alarm is established, 
which is the time to failure (i.e., trip) of a particular unit being 
monitored. Generally, this time will be the same for all channels. 
The next step in the program is to read in full-scale units for each 
monitor and the engineering units from the manual programmer 46. This 
determines: (1) the time period between scheduled automatic data log 
print-outs (i.e., one hour, eight hours, etc.); (2) data log print-out 
upon receipt of a trip, alarm or trend alarm signal; and (3) automatic 
spectrum analysis print-out upon receipt of a trend alarm, a trip signal, 
or an alarm signal. A scaling factor for full scale is then entered which 
corrects the stored overall value for full-scale readings. This is 
followed by the manual data log, manual trend and manual analysis input 
commands. At this time, the conditions of switches 100-106 are examined by 
the central processing unit 88 to determine if a manually-activated 
print-out has been commanded. The alarm trend for all channels is then 
computed and stored with the last four hourly-readings of vibration level 
from multiplexer 24. 
FIGS. 2 and 3 illustrate the manner in which the trend alarm is calculated. 
From FIG. 2, it can be seen that the vibration amplitude from a particular 
monitor has risen over five successive hours. At the 6th hour, the signal 
received at the first hour is removed from storage and the 6th-hour signal 
is inserted. However, before the first-hour signal is removed, it is 
averaged with the first through fifth-hour signals. Likewise, the second 
through sixth-hour signals are averaged. From these two averages, the 
computer establishes, in effect, a straight line 112 and calculates the 
slope of that line. Whether or not an alarm trend signal will be generated 
is achieved by calculating, through a simple trigonometric relationship, 
the time between the last average point and an intersection of line 112 
with an established trip setpoint 114. If the calculated time is equal to 
or less than a predetermined time stored in the random access memory 92 
(which is the same for all channels), then automatic input-output occurs 
for the channel in question as well as a vibration analysis for that 
channel and a data log on all monitors associated with a piece of 
equipment from which the trend alarm was signaled. The final steps in the 
program comprise analysis print-out, data log print-out, trend alarm 
print-out and system alarm print-out, in which steps the printer is 
commanded to print-out data stored in the random access memory 92. 
Typical print-outs from the printer 94 under certain conditions are as 
follows: 
______________________________________ 
CONDITION PRINT-OUT 
______________________________________ 
Normal Periodic Data 
Data Log 1.phi.17 .phi.25 
Log or On Command 
.phi.1 .phi..15 G 
Via Touch Switch 
.phi.2 .phi..10 G 
.phi.3 .phi..81 MIL 
.phi.4 .phi..07 I/S 
.phi.5 .phi..18 MIL 
47 .phi..25 MIL 
48 .phi..30 MIL 
Spectrum Analysis 
Analysis 2.phi.31 .phi.9.phi. CH21 
on Command Via Overall .phi..8 1 MIL 
Touch Switch 1476 .phi..1 2 --- 
1582 .phi..1 9 ---- 
1696 .phi..4 3 ---------- 
1817 .phi..3 9 --------- 
1946 .phi..1 6 ---- 
3163 .phi..2 2 ----- 
3391 .phi..2 8 ------- 
3634 100 .1 8 ---- 
- 4171 .phi..1 .phi. 
48.phi..phi. 
- .phi..1 .phi. 
5146 .phi..1 1 -- 
689.phi. .phi..1 2 --- 
Trend on Command 
TREND ALARM 1.phi.12 .phi.95 CH15 
via Touch Switch 
INF HOURS TO TRIP 
Automatic Vibration 
Analysis .phi.1.phi.7 31.phi.CH11 
Analysis & Data Log 
Overall .phi.9.3 MIL 
Upon Receipt of 
1378 .phi.2.5 MIL ------ 
Alarm or Trip Signal 
1582 .phi.1.7 MIL ---- 
1817 .phi.4.6 MIL ----------- 
6430 .phi.4.1 MIL ---------- 
DATA LOG 
.phi.3 5..phi..phi. MIL A*TD 
.phi.4 .07 I/S 
.phi.11 1..phi..phi. I/S T*TD 
.phi.24 .phi..78 MIL 
.phi.25 6.22 MIL A* 
SYSTEM TEST SYSTEM ALARM .phi.815 225 
SYSTEM NORMAL .phi.816 225 
______________________________________ 
The first print-out above is normal periodic data log or a data log which 
can be on command via the touch switch 102. The number 1017 indicates that 
the print-out occurred at the 10th hour and 17th minute of the day in 
question; and the number 025 indicates that the print-out occurred on the 
25th day of the year. The condition of each channel is printed out beneath 
the date and time. For example, channel No. 1 prints out 0.15 G's. The 
arithmetic unit involved for this particular channel was determined by the 
manual programmer 46 as are the arithmetic units for all of the other 
channels. Channel No. 3, for example, prints out 0.81 MILS whereas channel 
No. 4 prints out 0.07 inch per second and represents a signal derived from 
an accelerometer pickup. 
The next print-out represents a spectrum analysis for a particular channel 
on command via the touch switch 104 of FIG. 1. The print-out shows that 
the analysis occurred at the 20th hour and 31st minute of the 90th day of 
the year and is for channel No. 21, this being determined by the touch 
switches 96 and 98 in FIG. 1. The print-out shows that the overall signal 
level (i.e., for all frequencies) is 0.81 MIL. Following this is a 
print-out of the specific amplitudes at various predetermined frequencies 
which are initially determined in the manual programmer 46. In the example 
shown, samples are taken at 1476, 1582, 1696, etc. cycles per minute. From 
this analysis, and from previous experience with the vibrating equipment 
in question, the general condition of the equipment can be determined. For 
example, excessive amplitude at one frequency can indicate a lubrication 
problem. The tips of the dashed lines to the right of the amplitude 
readings give an approximte visual representation or plot of the spectral 
response of the input signal. Each dash represents a full 0.04 mil 
amplitude such that the line for 0.43 mils, for example, contains 10 
dashes, that for 0.39 mils contains 9 dashes, etc. 
The next two print-outs in the foregoing example are trend on command via 
the touch switch 106 of FIG. 1 and an automatic trend alarm. In the trend 
on command, the print-out indicates that for channel 15, preselected via 
the switches 96 and 98, there are an infinite number of hours to trip at 
10:12 A.M. on the 95th day of the year and that the equipment being 
monitored is operating satisfactorily. The next print-out is an automatic 
vibration analysis and data log upon receipt of an alarm or trip signal 
from any monitor. This automatic analysis occurred on the 310th day of the 
year at 1:07 A.M. for channel 11. Following the print-out of the vibration 
analysis at preselected frequencies is a data log for only those monitors 
associated with the equipment from which the alarm or trip signal was 
received on channel 11. These comprise monitors 3, 4, 11, 24 and 25 
preselected in the manual programmer 46. The "T" for channel 11 shows that 
this channel went into a trip condition and the "A" for channel 3 shows 
that this channel went into an alarm condition. The "TD" signifies that 
both channels 3 and 11 are in a trend alarm condition also. The asterisk 
indicates a change in that channel's condition. When the fault condition 
is reset, an automatic data log will follow, with only the asterisk 
present (i.e., without the "T", "A" or "TD" designations). 
Finally, a system test print-out occurs when touch switch 100 is depressed. 
As was explained above, the system test provides for checking of internal 
circuit faults sensing by momentarily altering the internal test voltages 
via the touch switch 100. The print-out indicates system alarm and system 
normal as test voltages are altered, then returned to normal. An automatic 
system alarm occurs when an external monitor system circuit fault relay is 
energized while a system normal will result when the external relay is 
released. Also, an automatic system alarm occurs if a malfunction in the 
data acquisition system is detected. A system normal will result when the 
malfunction is corrected. 
Although the invention has been shown in connection with a certain specific 
embodiment, it will be readily apparent to those skilled in the art that 
various changes in form and arrangement of parts may be made to suit 
requirements without departing from the spirit and scope of the invention.