Data Logger Glossary

4–20mA loop - A common industrial measurement standard. A transmitter controls a current in the range of 4 to 20mA as a function of the measured parameter. Any receiver(s) or indicator(s) placed in series can output a reading of the parameter. The main advantage is 2-wire connection and high immunity to noise pick-up which is useful in industrial applications or where long cable runs are required. The transmitter(s) are often powered from a 24V supply.

50/60Hz rejection - The most common source of noise is that induced by AC line power from nearby cables or equipment. This noise is periodic at the line frequency which is 60Hz in the US or 50Hz in other parts of the world. Many data loggers are able to reject most of this noise by performing an integrating measurement of the input for exactly one line cycle period (16.7ms or 20ms).

Ω - ohm, a unit of resistance

μA - microamp, one millionth of an Amp

μs - microsecond, one millionth of a second

μStrain - microstrain, strain expressed in parts per million (ppm). Strain is a measure of the stress-induced change in length of a body.

μV - microvolt, one millionth of a volt

A - Ampere or amp, a unit of current

ADC Analog-to-Digital Converter. Part of the data logger that converts an analog input voltage to a digital number (in other words, it converts a smoothly-varying signal to a quantised digital value). Data loggers are a digital instruments, and therefore require an ADC to convert analog sensor signals into digital form prior to processing. Important characteristics of an ADC are its linearity, resolution, noise rejection and speed.

Ah - Ampere-hour, a unit of electrical charge, often used when referring to battery capacity

analog - a quantity that can vary continuously through a potentially infinite number of values — for example, the time swept out by the hands of a clock, or the output of a thermocouple. Compare with digital where the output can only assume a finite number of specific values 1, 2, 3, etc.

ASCII - American Standard Code for Information Interchange. A coding system designed for standardising data transmission to achieve hardware and software compatibility. It assigns a 7-bit code to each of the 128 standard characters: 96 visible characters — letters, numbers and punctuation marks (including the space character); 32 hardware control characters — sounding a bell, advancing a printer page, carriage return, line feed and so on.

asynchronous - Not synchronized to any regular event, not occurring at pre-determined or regular intervals. In an asynchronous communications channel, data is transmitted intermittently at random times rather than in a constant stream at a regular rate.

autoranging -The process of changing amplifier gain automatically so that the signal is amplified as much as is possible without exceeding measurement limits.

bit - The smallest unit of information in a computer. A bit has a single value: either 0 or 1. Computers generally store information and execute instructions in bit-multiples called bytes (8 bits).

bps - bits per second, a measure of data transfer rate

bridge - A sensitive and stable electrical device consisting of 4 elements that is used for measuring small changes in resistances. They are particularly useful when applied to strain gauges (as found in pressure sensors and load cells).

buffer - An area of memory where data is held temporarily until the system is ready for it, or in case it is needed in the future.

byte - A unit of information that is eight bits long

chochkes - Marketing term for lame or useless stuff that is often given away at trade shows or for other promotions