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Add/Subtract - A count operating mode in which two count inputs are provided. One input is used for adding counts (also referred to as counting up), the other input is used for subtracting counts (also referred to as counting down). Although two separate independent sensors may be used to provide a difference count, the most common means of counting employs a single sensor connected to one input to cause the counter to count up or down. Alarm - A condition that indicates that the process has either exceeded or fallen below the set point of that process. Alternating Current (AC) - An electrical current that changes directions at regular intervals. AC is the most efficient means of transmitting electrical power from the utility to the user and can be used as the count signal for some electric counters. Most electronic counters require AC as the source of power, but convert the AC to direct current (DC) for all internal functions. One sensor, the magnetic pickup, produces an alternating current output which requires special processing to be used by electronic counters and ratemeters. Analog - An electrical signal which varies in magnitude of current or voltage. Sensors such as flow meters and load cells increase/decrease the voltage or current output proportionally as the flow rate or weight increases/decreases. Analog signals must be converted to digital signals by an analog to frequency converter to be used by electronic counters and ratemeters. 4 - 20mA and 0-10V are the two most common analog signals. Auto Recycle - When a counter reaches its final predetermined count (either a preset value when counting up or zero when counting down), this feature returns the count to the starting point (either zero when counting up or a preset value when counting down). Auto Reset (Integral) - A feature of the controller that continuously compensates for droop by integrating errors over time and adjusting the proportional band appropriately. Auto Tuning - The ability of the controller to automatically calculate its own PID parameters to best fit the characteristics of each thermal system. Batch Counter - A second counter, usually internal, that counts the total number of cycles completed by the main counter. Batch counters count up only and are usually presettable so that when the required number of batches or pieces have been completed, the process can automatically stop. Baud - A serial data transmission rate (bits per second). Binary - Numbering system based on 2s instead of 10s. Digits used in the binary numbering system are 0 to 1. Bit - Binary digit. The smallest unit of information in the Binary Numbering System, represented by the numbers 0 and 1. Bounce Filter - The electronic circuitry used to eliminate the effects of bounce of mechanical switch contacts. The relatively high frequency bounce signal is filtered from the relatively low frequency contact closure count signal either by a resistor - capacitor network (hardware rolloff), or by microprocessor based software de-bounce. Byte - A sequence of binary digits usually operated as a unit. (The exact number depends on the system, but usually 8 bits.) CMOS - Complementary Metal Oxide
Semiconductor. An integrated circuit (IC) characterized by low quiescent power
drain, high speed operation, and high noise immunity. High noise immunity
makes CMOS the most commonly used IC family in electronic counters in
industrial applications. Chip - A tiny piece of semiconductor
material on which microscopic electronic components are photo-etched to form
one or more circuits. After connection leads and a case are added to the
chip, it is called an Integrated Circuit. Coincidence - The event which occurs when the
counter counts to the preset value in reset to zero mode or zero in reset to
preset mode. Coincidence is when relay and/or transistor outputs occur and
when auto recycling takes place, if used. Control Accuracy - The ability of
a complete system to maintain a process at the desired setting. Count - A digital signal or pulse which
causes a counter to increment or decrement. Count Doubler - A counter circuit which senses
both leading and trailing edges of a pulse, doubling the pulses utilized by
the counter. It is most commonly used to get increased resolution in
measuring applications. A 600 pulse per revolution encoder driven by a 12
inch circumference wheel will cause a counter to count in .01 inch increments
with count doubling and .02 inch increments without. Count Speed, Maximum - The maximum rate at which a
counter will respond accurately to the incoming pulses. Counter - A mechanical, electromechanical
or electronic device which keeps track of the number of input signals or
pulses. Current - The rate of electron flow (measured
in amperes.) One ampere flows through a one ohm resistor when one volt is
applied. Current Sink - A sensor output which provides
a current path to DC common when it is on. Current flow is from the counter
into the sensor. Most commonly an NPN transistor or contact closure to DC
common. Current Source - A sensor output type such that
when it is ON, current flow is from the sensor into the load (PNP Transistor
or contact closure to V+). Cycle Time - The time required for a
controller to complete one On-Off cycle. Diffuse-Reflective
Photo Sensor
- An emitter-receiver combination that emits modulated, infrared light
(emitter) and detects the presence of objects by picking up modulated,
infrared light reflected by them (receiver). Digit - Each character or figure in a
counter display, i.e., a five digit readout is a display with five figures. Digital - Electronic circuit or device
where the signal exists in only one of two states, ON or OFF, also known as
high or low, 1 or 0, mark or space. Diode - An electronic device which
allows current to flow through it in one direction only. Direct Current (DC) - A current or voltage that does
not change polarity. Electronic counters operate on DC, either from a battery
or derived from alternating current (AC). Excess Gain - The ratio of optical power
available at a given emitter-receiver range, relative to the minimum optical
power required by the receiver for triggering. Ferrous - A metal composed of and/or
containing iron. A magnetic pickup "senses" ferrous material only
passing by it; inductive proximity sensors detect ferrous material at a
greater range than other conductors. Frequency - Number of cycles per second of
a waveform. The unit of frequency is Hertz (Hz). Fuzzy Logic - A linguistic control that controls
a system based on experience and data collected over time. It attempts to
model what the human response would be and apply the most intelligent
solution to deal with the error involved with PID controllers. Ground - A conducting path between an electric
circuit or equipment and the earth. Hertz (Hz) - The unit of frequency. One
hertz equals one cycle per second. In counting, the repetition rate of a
count signal in counts per second. Hysteresis - The temperature sensitivity
between the on and off switching points that is designed into the control.
Hysteresis is usually expressed in percent. Hysteresis, Switching - The characteristic of an object
that once changed by an external force, it takes a greater force in the
opposite direction to restore that object to its original state. For a count
input, 1/3 of the input voltage (Vcc) or less may be considered the low state
and 2/3 Vcc, the input is considered the high state. When the input voltage
is between 1/3 Vcc and 2/3 Vcc, the input is considered low or high depending
upon where it was previously. Once high, the high state lasts until the
voltage has dropped to 1/3 Vcc. Once low, the low state lasts until the
voltage has risen to 2/3 Vcc. This is used to reduce the effects of
electrical noise on count or control input signals. I - J Infrared - The invisible light that
certain LEDs emit, usually modulated. Photo sensors use infrared light
because they are unaffected by ambient, visible light. Integrated Circuit
(IC) - An
interconnected array of active and passive elements within a single
semiconductor, sold as one package. Kilo - 1,000; when related to maximum
counting speed (kHz), thousands of counts per second. Lead Zero Blanking - The blanking of all zeros in the
counter display to the left of the most significant digit, or decimal point
holding digit; i.e., 0.01. Electronic counters use lead zero blanking to make
the display easier to read. Leakage Current - A small current flowing through
a transistor in the OFF state. Level - A step in a sequential
controller’s program. Each level processes a count or time instruction along
with outputs or executes a jump or repeat instruction. When applied to
counters, the number of levels refers to the number of presets in the main
counter. See Preset. Light Emitting Diode
(LED) - A
semiconductor diode that can serve as a light source when voltage is applied
to it. Commonly used for indicator lights, numeric displays and for optically
isolating data inputs. Liquid Crystal Display
(LCD) - A
display device consisting basically of liquid crystal fluid sealed between
two glass plates. The readout is either dark characters on a dull white
background or white on a dull black background. An LCD display consumes much
less power than a LED display, making it desirable for battery powered
counters. An LCD dot matrix display can also be used for alphabetic and
graphic characters. An LCD display may be backlit by LEDs to provide
readability in dark installations. Low Speed Counter - A counter input or mode used to
eliminate the effects of mechanical switch bounce. Memory - A grouping of circuit elements
which has data storage and retrieval capability; i.e., ROM, RAM, EPROM,
NovRAM. Microprocessor - An electronic computer
processor section implemented in relatively few IC chips (typically LSI) that
contains arithmetic, logic, register, control, and memory functions. Millisecond (mS) - One thousandth of a second:
0.001 second. Modulated - When applied to photo-sensors,
it means that the emitter LED is turned ON and OFF very rapidly and the
receiver is synchronized to pick up only reflected light that its LED
emitted. Nema Enclosure Ratings - Provide mechanical and
electrical protection for operator and equipment. Brief descriptions of the
various enclosures are given below. NEMA Standards Publication No. 250 - 1979
gives more comprehensive descriptions, definitions and/or test criteria. Nema Type 1 - For indoor use. Used for
applications where unusual service conditions do not exist but where a
measure of protection from accidental contact with enclosed equipment is
required. Designed to meet tests for Rod Entry and Rust Resistance. Nema Type 4 - For indoor use. Provides
protection from splashing water, hose-directed water, and dust. Constructed
of sheet steel or plastic with gasketed cover. Designed to meet tests for
Hose Down, Dust, and Rust Resistance. Nema Type 12 - For indoor use. Provides a
degree of protection from dripping liquids (non-corrosive), falling dirt and
dust. Designed to meet tests for Drip, Dust and Rust Resistance. Nema Type 13 - For indoor use. Provides dust
protection and protection against water, oil or non-corrosive coolant spray.
Designed to meet tests for Oil Exclusion and Rust Resistance. Noise, Electrical - Noise is undesirable electrical
voltages or currents. It can cause counters to operate erratically, produce
false counts, or cause counter failure. Noise Immunity - The ability of counter circuits
to reject undesired electrical signals. Nonvolatile Memory - A memory that does not lose its
information while its power supply is turned off. Ohm - The unit of electrical
resistance. One-Shot - An input that causes an output
that cannot be reenergized until the input has turned off and reoccurred. One
shot inputs are also known as edge-sensitive inputs. On/Off Control - A temperature controller that
operates with a scheme where the output is either fully on above the set
point or fully off below the set point. Open Collector - An NPN transistor with its
emitter connected to DC common, and its collector as the output. When the
transistor is off, it acts like an open switch. When the transistor turns on,
it looks like a closed switch, sinking current from the load to DC common. Parallel Circuit - A circuit in which current has
two or more paths to follow. Two electrical elements are in parallel if both
terminals of both elements are connected plus to plus and minus to minus. Photosensor - A sensor device consisting of a
source of light (emitter) and a light sensitive switching element (receiver).
The sensor detects the presence of opaque or translucent objects either when
the beam from the emitter to the receiver is broken (dark sensing photo
sensors), or when emitted light is reflected back to the receiver (light
sensing photo sensors). Photo sensors are available with either and the
output may be normally opened (NO) or normally closed (NC). PID - A control mode with
proportional, integral, and derivative action. Proportional action dampens
the response to the system, integral action corrects for system droop, and
derivative action tries to prevent overshoot and undershoot. Preset - A predetermined count value
programmed into the counter by the user. The event at which the counter
counts to the preset is called coincidence, which causes outputs from the
counter and may also auto recycle. A counter with one or more presets is
considered a count control since it gives the user control output capability
based upon a count value. Non-presettable counters are called totalizer
counters since they merely count and cannot produce outputs based on count.
Presets are also referred to as levels or setpoints. Preset Mode - A counting mode where counting
is generally subtractive. The counter resets or auto recycles to the preset
count. When the counter counts to zero, the output associated with the preset
number occurs. Prewarn - Refers to preset value settings
which are set a few counts short of the final preset. It is used to provide a
warning or slow-down output for control of material movement or liquid flow
before the last output occurs. Proximity Sensor - A device used to sense the
presence of conductive material especially metal. Proximity sensors do not
make physical contact with the target; they produce an electric field which
is altered by the presence of the target. Their relative high switching speed
and low cost make them very popular count and control input sensors. Pulse - A momentary sharp change in
current and voltage. A count pulse is a square wave, or a rectangular wave.
Pulses are digital signals; the voltage or current is either "on"
or "off." Quadrature - A count operating mode which senses
both distance or amount and direction. This mode of counting provides
anti-jitter protection and measurement of materials in two directions.
Typically quadrature encoders are used; however, other sensors used in pairs
can be physically arranged to provide quadrature counting. Rate - Generally, anything per unit of
time. Examples: RPM, ft/min, barrels/hour. Rate Difference - The difference or subtraction
of two rates. It can be expressed as Rate A - Rate B. In a flow application,
for example, diesel fuel is pumped to an engine at a relatively constant
rate. Whatever is not consumed by the engine is returned to the tank by a
separate line. With flow meters in both in and out lines, the rate of fuel
consumption is the rate out to the engine minus the rate back into the tank. Ratemeter - A device that monitors and
displays rate. Ratio - The comparison of two rates: Ratio Difference
(DRAW) -
The difference of two ratios, this can be expressed as Read - The process of taking
information from memory. Rectifier - A device that converts
alternating current into direct current. See Diode. Reset - A remote input or front-panel
switch closure which causes the counter to return to an initial value. This
value can be either zero or to a number set in as a preset value. The auto
recycle function does this task internally within the counter. Reset Mode - A counting mode where generally
counting is additive and outputs occur when the count matches the preset
value. The counter presets or auto-recycles to a value of zero in this mode
of operation. Reset to Preset - Causes the counter to return to
the value of a preset number. Resistance - The opposition that a device
offers to the flow of electrical current, measured in ohms. Resolution - The incremental size of a unit
of measure. As the unit of measure is divided into smaller parts we obtain
better resolution, i.e., 1 inch divided by 100 = 0.01". 0.01" has
100 times better resolution than 1" in cutting and measuring
applications. RTD - A control mode with
proportional, integral, and derivative action. Proportional action dampens
the response to the system, integral action corrects for system droop, and
derivative action tries to prevent overshoot and undershoot. Scaler - A multiplier that is applied to
each input pulse which allows a counter to be programmed in and displayed in
units such as inches or gallons and allows a ratemeter to display units such
as inches/second, or gallons/minutes. Schmitt Trigger - Converts a slow rising or
falling signal input to a digital output at a preselected signal point.
Schmitt triggers provide hysteresis for improved noise immunity. See
Hysteresis. Semiconductor - An electronic device that
either conducts current or blocks current. A diode conducts current in the
forward direction and blocks reverse current. A transistor conducts current
collector to emitter when a base current is applied and blocks current
collector to emitter when the base current is not applied. Sensor - An input device that monitors a
process parameter to provide a count or control input to the counter. Series Circuit - A circuit in which current has
only one path to follow. Elements in a series circuit are connected plus to
minus, etc. Setpoint - See Preset. Signal Conditioning - To change the form of a signal
to make it compatible with a count input circuit, including such manipulation
as pulse shaping, digitizing, and linearizing. Signal conditioning can also
convert a sourcing signal into a sinking signal. Solid State Relay
(SSR) - A
solid state switching device with no moving parts that switches current on
and off. Span - The absolute value of the
difference between a controller's upper and lower limits. Tachometer - Ratemeter that specifically
displays RPM. Thermocouple (T/C) - A temperature sensor
constructed of two dissimilar metals. At the junction, the two metals produce
a voltage proportional to the difference in temperature between the hot
junction and the lead wires (cold junction) connected to the sensing device. Thermal System - An environment
consisting of a sensing device, a heat source, a heat transfer medium, and a
temperature controller designed to provide heat. Time Base - A method of determining rate by
counting pulses for a set period of time, updating the display with the pulse
count, then resetting the counter and counting pulses for the next rate
update. The time base setting is called the update time. Time Out - Timers that control the length
of time an output is actuated. Totalizer - Generally a counter that can
accumulate counts but cannot control a machine. Some totalizers are
presettable, but their primary function is to keep track of counts over a
relatively long period of time. Transducer - Converts one form of energy to
another. Example: a magnetic pickup converts mechanical energy into
electrical energy which a ratemeter may use as its input signal. Up/down Counter - A counter that can count either
up or down. Up/down counters have two count inputs and are used in
add/subtract, quadrature, or count with direction control modes. Volatile Memory - A memory that loses its
information if the power is removed from it. A RAM is volatile unless it is
battery backed-up. Volt - A unit of potential
(electromotive force.) One volt causes one amp of current to flow through one
ohm of resistance. Voltage - Term used to designate the
electrical energy differential that exists between two points and is capable
of producing a flow of current when a closed path is connected between the
two points. Voltage Transient - A short duration voltage spike
sometimes many times larger than the supply voltage, usually caused by the
operation of heavy inductive loads such as motors, contactors, and solenoids;
can cause noise problems in fast electronic circuits such as solid state
counters. W - X - Y - Z Word - A number of bits in a sequence
that is treated as a unit. Waveform - A shape obtained by displaying
a voltage or current as a function to time usually on an oscilloscope. AC
line voltage produces a sine wave shape. Count signals are square, or
rectangular. Write - The process of loading
information into memory. |