Same as large, but allows data segments that are larger than 64K bytes.</div>
- Large type
- Both code and data fit into multiple code and data segments.
- A low pass filter only allows low frequency signals to get to the measurement hardware
- high frequency (noise) signals are attenuated. Filters have the disadvantage of
slowing down the response the signal.
- Least Significant Bit
- All code fits into a single 64K byte code segment, and all code fits into more than
one 64K byte code segment. This allows code to exist in multiple segments.
- All code fits into a single 64K byte code segment and all code fits into another
single 64K byte code segment. This allows all code to be accessed with near jumps
and calls.
- All data and code fit into one segment, the code segment. Tiny model programs are
written in the .COM file format, which means that the program must be originated
at memory location 0100H. This model is most often used with small programs.
- Most Significant Bit
- A multidrop communication line connects multiple devices together on a common transmission
line for communication with each other.
- Multiplexers are electronic devices that are used to switch multiple channels to
a single measurement instrument, one at a time. They operate much the same way as
television set; although several channels are available, only one channel is viewed
at a time.
- A communication link between PLCs, workstations, industrial equipment, and other
devices.
- Voltage differentially between two wire that appears to be part of the input signal.
The noise is the most difficult to eliminate because it appears to be part of the
signal. Normal mode noise can occur as a result of common mode, electrostatic, or
electromagnetic noise finding its way to the signal. In most cases, the noise is
related to AC power lines. If so, it appears as a 50 or 60 Hz sine wave added to
the DC voltage that we want to measure. A filter can be used to reduce 50 or 60
Hz but the slow response of the filter will slow down the measurements speed. Filters
also inject some errors of their own.
TIP : The best way to eliminate power line noise is with
an integrating voltmeter. The noise signal is integrated out with only minimal loss
of speed.
- Negative Temperature Coefficient
- ON/OFF control is the simplest of control. A switch card is used as the control
hardware to turn something on or off.
- Open-loop control is generally used in the characterization of a product or process.
The product, for instance, is run through a series of tests and the results are
collected.
- Optical isolators are used with digital circuitry to shield high voltage signals
from affecting digital circuitry.
19 inch Rackmount Adapter for PCLD-series Daughterboards(3 units wide).
- A PID controller or PID loop, constantly reads and manipulates an output condition
so that a process variable is maintained at a set-point.
- The PID algorithm combines P-value proportional to the error value, I-value a time
integral (accumulation of past errors), and D-value a time derivative (rate of change)
of the error value. The P, I, and D factors may vary depending on the process being
controlled.
- PID control has the advantage of being able to respond to rapidly changing errors
before they get too large and yet send out control values that will not cause the
process to overreact.
- A standard hardware device to control plant startup, running and shutdown sequencing,
which may be readily altered to suit changed operating conditions.
- PLC are electronic replacements for traditional industrial hard-wired relay panels.
Available from a wide variety of manufacturers for all purposes, PLCs offer more
control and are much easier to install and use than relay panels.
- The pulse output card is a combination of a digital output card and an arbitrary
waveform generator. Like the waveform generator it contains a clock. It outputs
a series of pulses at varying rates. The most common use of a pulse output card
is to control stepper motors.
- Polling is the simplest method for detecting a unique condition and then taking
action. This involves a software loop that contains all of the required measurement,
analysis, decision-making algorithms and planned actions. The data acquisition program
periodically tests the system‘s clock or external trigger input to sense a
transition. Whenever a transition occurs, the program then samples each of the inputs
and stores their values in a “frame”. A frame is simply a list that
contains the values representing the specified inputs at a given time. The frames
can be stored in RAM, disk or other types of memory. Each time the program senses
a clock “tick”, the inputs are scanned and converted, and a new frame
is added to memory. In this mode, generic PC/AT’s can support an acquisition
rate of about 10Khz.
- In addition, the PC is continuously busy when the polling loop is operational, and
hence no other tasks can be serviced. When an application cannot tolerate these
characteristics, interrupt techniques may be needed.
- Electrical interference caused by radiation from power cables or machinery in the
vicinity of the signals to be measured.
- The pseudo-differential configuration brings the common lines of all channels back
to the systemsymbol 145 \f "Times New Roman"s front end on two lines :
AGND and IN LO. Choose pseudo-differential inputs over single-ended inputs whenever
your setup can accommodate more than one ground wire.
- If your sensor is not grounded, you should install a resistor between IN LO and
AGND. You should also install a resistor between each channelsymbol 145 \f "Times
New Roman"s input line and AGND. The resistors will protect your system from
common mode voltages. Any induced currents in the sensor line will travel down the
low impedance AGND line to ground and away from the high impedance IN LO line, ensuring
the integrity of your measurements.
- Pulse Width measurements are used to determine the length of time a pulse stays
at a high (or low) voltage level. One practical application is to use a sensor and
measure the amount of time it takes an objects to pass this sensor. This measurement
can be used to determine the speed of a known object or if speed is known, the length
of an object where size is not known.
- Platinum Resistance Temperature Detector
- A temperature transducer RTD made by platinum metal.
- Rectifiers are used to convert an AC signal into a DC signal. Some application call
for an AC measurement. If your A/D converter does not measure AC signals, a rectifier
would be needed to convert the signals to DC voltage levels.
- Simple relay configurations may be used in applications from the power to the device
under test (DUT) to forming a complex matrix topology for measurements. Some of
the most common configurations consist of from A, form B, and form C configurations
which can be linked together to form binary switching networks which guarantee that
only one point can be connected to any other point at a time. Similarly, these can
be configured to form measurement buses for the connection of many points to one
point at a time. For the most part, this configuration is used for simple on-off
switching of power rather than signals.
- Resolution is the smallest change that a measurement instrument can sense. Resolution
is normally specified in bits.
- RS-232 a low-cost and reliable standard for low speed, point to point communications
at distances up to 50 feet (15 meters). The biggest drawback to RS-232 communications
is that plant floor environments often generate electrical noise and transients
which can cause errors in transmission and damage to the interface components.
- RS-422 communications, with its balanced transmission and receiving modes, improve
the reliability of transmitted data to make RS-422 preferred over RS-232 communications.
Additionally, RS-422 communications allow you to specify a master workstation for
multidrop connections to create a small network. The RS-422 standard permits transmissions
up to 4000 feet (125 meters).
- The RS-485 standard includes all of the improved communications features of RS-422,
but also allows you to operate using multiple master workstations with only a smaller
and less expensive communication cable. half duplex, differential signal, two wire
connection
- A transducer that changes resistance proportional to its temperature. Its advantages
are most stable, most accurate, and more linear than thermocouple. Its disadvantages
are expensive, slow response time, current source required, small resistance change,
4 wire measurement, and self-heating.
- RTD requires a four-wire ohms measurement in order to get a reliable reading, especially
if the RTD is located several feet from the DAC system.
- Resistor Transistor Logic
- Request To Send
Handshaking signals, are normally used to control the direction of the data flow
for RS-485.
- SCADA is the name applied to the control of pipe lines, production wells, etc.,
through telemetry to a central computer.
- When two wires composed of dissimilar metals are joined at both ends and one of
the ends is heated, there is a continuous current which flows in the thermoelectric
circuit. Thomas Seebeck made this discovery in 1821. If this circuit is broken at
the center, the net open circuit voltage (the Seebeck voltage) is a function of
the junction temperature and the composition of the two metals. All dissimilar metals
exhibit this effect.
- A single-ended configuration is best when you need to make analog measurements with
respect to a common external ground. This configuration is also appropriate when
there is no practical way to bring both a signal ground and an analog ground (AGND)
back to the systemsymbol 145 \f "Times New Roman"s input terminals.
- Device that converts a physical parameter such as temperature, pressure, flow, strain,
or position into an electrical signal - sometimes used synonymously with transducer
- a true sensor contains signal conditioning so its output is more easily measured.
- Measurement hardware that is used to capture events on multiple channels - when
triggered, hardware will hold value of input until a measurement can be made.
- An extra layer of conductive material surrounding a wire to prevent external electrical
signals from interfering with the signal on the wire.
- To electrically amplify, reduce, eliminate, or change a signal - used to alter signals
(eliminate noise) before they are measured in order to get more accurate measurements.
- SPC is a tool used to improve productivity and reduce costs.
- SPEC benchmarks are to workstations what FFTs are to DSPs - the most popular metric
of performance comparison.
- Single-Pole Dual-Throw relay
- Single-Pole Single-Throw relay
- SQC is a tool used to improve productivity and reduce costs.
- Structured Query Language
- Solid State Relay
- Electro-mechanical device that rotates(or moves) proportional to pulses it receives
from a stepper motor controller - DAC system sometimes contain stepper motor controllers
- used for positioning equipment.
- Change in length of a material divided by its total length - strain measurements
are used in order to calculate the stress on a material.
- The successive approximation A/D is less expensive than a flash converter. It uses
one comparator and generates reference voltages, comparing each one to the input
signal. If the input signal is varying a voltage error can occur.
- A switch is a mechanical or electronic device that is used to maker or break the
connections in an electrical circuit. Switches can be used to route the output signals
from multiple transducers to one measurement instrument (scanning). Switches are
also used as control devices to switch power to external fans, heaters, pumps, lights,
and motors.
- A pair of dissimilar conductors that are connected together at a point and produce
a voltage proportional to temperature. Its advantages are self-powered, simple,
rugged, inexpensive, wide variety of physical forms, and wide temperature range.
Its disadvantages are non-linear, low voltage, reference required, least stable,
and least sensitive.
- When two wires composed of dissimilar metals are jointed as both ends and one of
the ends is heated, there is a continuous current which flows in the thermoelectric
circuit. Thomas Seebeck made this discovery in 1821.
TIP : Do not attach thermocouple wire directly to your
voltmeter. Use an isothermal block.
- Platinum -6% Rhodium (+) Versus Platinum -30% Rhodium (-)
- Seebeck coefficient = 6 mV/°C, and DVM sensitivity for 0.1°C = 0.6 mV, Range
= 0°C to 1820°C, 4.4 ~ 8.6°C standard wire error.
- Nickel -10% Chromium (+) Versus Constantan (-)
- Seebeck coefficient = 62 mV/°C, and DVM sensitivity for 0.1°C = 6.2 mV,
Range = -100°C to 1000°C, 1.7 ~ 4.4°C standard wire error.
- Iron (+) Versus Constantan (-)
- Seebeck coefficient = 51 mV/°C, and DVM sensitivity for 0.1°C = 5.1 mV,
Range = 0°C to 760°C, 1.1 ~ 2.9°C standard wire error.
- Nickel -10% Chromium (+) Versus Nickel - 5% (-) (Aluminum Silicon)
- Seebeck coefficient = 40 mV/°C, and DVM sensitivity for 0.1°C = 4.0 mV,
Range = 0°C to 1370°C, 1.1 ~ 2.9°C standard wire error.
- Nicrosil (+) Versus Nisil (-)
- Seebeck coefficient = 39 mV/°C, and DVM sensitivity for 0.1°C = 3.9 mV,
Range = 0°C to 1300°C
- Nicrosil (+) Versus Nisil (-)
- Seebeck coefficient = 26.2 mV/°C, and DVM sensitivity for 0.1°C = 2.62 mV,
Range = -270°C to 400°C
- Platinum -13% Rhodium (+) Versus Platinum (-)
- Seebeck coefficient = 7 mV/°C, and DVM sensitivity for 0.1°C = 0.7 mV, Range
= 0°C to 1000°C, 1.4 ~ 3.8°C standard wire error.
- Platinum -10% Rhodium (+) Versus Platinum (-)
- Seebeck coefficient = 7 mV/°C, and DVM sensitivity for 0.1°C = 0.7 mV, Range
= 0°C to 1750°C, 1.4 ~ 3.8°C standard wire error.
- Copper (+) Versus Constantan (-)
- Seebeck coefficient = 40 mV/°C, and DVM sensitivity for 0.1°C = 4.0 mV,
Range = -160°C to 400°C, 0.8 ~ 2.9°C standard wire error.
-Re type - Tungsten - 5% Rhenium (+) Versus Tungsten - 26% Rhenium (-)
- Seebeck coefficient = 19.5 mV/°C, and DVM sensitivity for 0.1°C = 1.95 mV,
Range = 0°C to 2320°C
- When two dissimilar metals are joined together and the temperature between the two
ends are different, it is very easily affected by the nearby device with extreme
change in high or low temperature. This temperature changes is called thermal noise.
- Transducers like RTDs, thermistors, and strain gages are devices whose output resistance
changes. All require power to make them work. When power is applied to a resistive
device, it heats up. The rise in temperature causes a change in resistance and an
error in the measurement.
TIP : To eliminate self-heating effects, do not apply
power to the device any longer than necessary.
TIP : For best results, make two measurements - one without
power applied to the transducer and one with power applied. Simple subtraction will
eliminate the thermal noise (self-heating).
- A piece of hardware to which wires coming from transducers connect to the data acquisition
system.
- Temperature transducer that changes resistance proportional to its temperature.
Its advantages are high output, fast response time, and two-wire ohms measurement.
Its disadvantages are non-linear, limited temperature range, fragile. current source
required, and self-heating.
- Time interval measurements can be made by the more sophisticated counters. These
measurements are the time between one edge of a pulse and another. If the edges
are both the same, the time interval is the period. If one edge is rising and the
other is falling, the time interval is equal to the pulse width.
- Devices that convert physical parameters such as temperature, pressure, flow, strain,
or position into electrical signals such as voltage, current, or resistance.
- Transducer can be used to measure temperature, pressure, flow, level, position,
pH, strain, and many other physical parameters. For example, a temperature transducer
may output a specific value at 50 degree C. As the temperature changes, the output
voltage changes.
- Transformers are normally used to step-down (reduce) large voltage and eliminate
ground loops (noise) in analog measurements.
- True Differential Input
- True differential operation provides a separate return line for each input channel.
Using this configuration cuts the channel count in half for a given data acquisition
board or system, but because it separates the return currents of each input, it
reduces the errors caused by noise.
- Although true-differential inputs offer the best immunity from ground noise, voltages
common to both a channelsymbol 145 \f "Times New Roman"s HI and LO inputs
can provide measurement errors.
- Terminate and Stay Resident
- TSR stay resident program is a program that remains in memory until it is activated.
- A program (TSR) remains in the memory system even after the program returns to DOS.
Access to a TSR is via the interrupt structure of the microprocessor.
- Transistor Transistor Logic