Lab Equipment Glossary
Plain-English definitions of the terms you'll meet when choosing and using lab equipment. Jump to: Weighing · Centrifuges · Mixing & heating · pH · Filtration & glassware · Solutions & units
Weighing
Readability (resolution, "d")
The smallest step a balance displays, e.g. 0.01 g. It is not the same as accuracy: a balance can display 0.01 g and still be off by more than that.
Accuracy
How close a reading is to the true mass. It depends on calibration, linearity, repeatability and the environment.
Repeatability
How closely repeated weighings of the same object agree, usually given as a standard deviation. It is the main limit on weighing small amounts.
Linearity
The largest deviation from a straight-line response across the weighing range after calibration, e.g. ±0.03 g. Good linearity means the balance is right at 10 g and at 2,000 g, not just at the calibration point.
Capacity
The maximum load the balance can weigh, including your container.
Tare
Zeroing the display with a container on the pan so you see only the net weight of what you add.
Minimum weight
The smallest sample a balance can weigh within a required accuracy. Because of repeatability, it is far larger than the readability. In regulated pharmaceutical work (USP chapter 41), it is calculated from measured repeatability; as a rough rule, weigh at least several hundred to a thousand times the readability for 0.1% accuracy.
Stabilization (settling) time
How long the reading takes to become stable after you place a load, typically 3–8 seconds.
Calibration
Adjusting a balance against a known reference mass so it reads correctly. External calibration uses a weight you place on the pan; internal calibration uses a built-in motorized weight.
Calibration certificate
A document recording how a balance read against reference weights at the time of testing, used for quality records and audits. See Understanding Calibration Certificates.
Weight class (F1, M1, etc.)
OIML accuracy classes for calibration weights. F1 weights have tighter tolerances than M1; the right class depends on the balance's readability.
Analytical balance
A balance reading to 0.1 mg (0.0001 g) or finer, with a glass draft shield. See analytical balances.
Precision (top-loading) balance
A balance reading to 0.1–0.001 g, usually with an open pan and higher capacity. See precision balances.
Draft shield
An enclosure around the pan that blocks air currents, essential at 0.1 mg readability.
Load cell / strain gauge
A sensor that measures force through the tiny deformation of a metal element. Common in precision balances and scales.
Electromagnetic force restoration (EMFR)
A sensor that measures mass by the electric current needed to hold the pan in place. Used in analytical balances for its high resolution.
Counting (PCS) mode
A function that counts identical parts by dividing the load by an average piece weight taken from a reference sample. See counting small parts.
NTEP / legal for trade
US approval (National Type Evaluation Program) required for scales used to sell goods by weight. Laboratory balances without it are fine for formulation, testing and inventory, but not for pricing goods at sale.
RS-232
A serial data port used to send readings from a balance or meter to a PC or printer for records.
GLP / GMP
Good Laboratory Practice and Good Manufacturing Practice: quality systems that require documented, traceable measurements.
Centrifuges
RPM
Revolutions per minute: how fast the rotor turns. On its own it doesn't tell you the force on the sample.
RCF (relative centrifugal force, × g)
The force on the sample as a multiple of gravity. RCF = 1.118 × 10⁻⁵ × r (cm) × RPM². Protocols should specify RCF, not RPM. Convert with our RPM to RCF calculator.
Rotor radius
The distance from the center of rotation to the sample (usually measured to the bottom of the tube for maximum RCF). It's needed to convert RPM to RCF.
Fixed-angle vs swing-out rotor
Fixed-angle rotors hold tubes at a set angle and pellet quickly; swing-out rotors let tubes swing horizontal, giving flat, even layers.
PRP
Platelet-rich plasma: blood plasma concentrated in platelets, prepared by centrifugation. See centrifuges.
Balancing a centrifuge
Placing tubes of equal mass opposite each other so the rotor spins without vibration. An unbalanced rotor can damage the centrifuge.
Mixing & heating
Viscosity
A fluid's resistance to flow. Water is about 1 mPa·s; honey is around 10,000 mPa·s.
mPa·s and cP
Units of viscosity. 1 mPa·s = 1 centipoise (cP), so the numbers are interchangeable.
Torque (N·cm)
The turning force a stirrer motor delivers. Higher torque keeps thick samples moving at speed.
Magnetic stirrer
A stirrer that spins a PTFE-coated stir bar from below with a rotating magnet. Best for low-viscosity liquids. See magnetic stirrers.
Overhead stirrer
A stirrer that drives a shaft and blade from above, for thick or large samples where a stir bar would stall. See overhead stirrers.
Decoupling
When a stir bar loses its magnetic grip and spins out, usually from too high a speed, too thick a sample or too large a vessel.
PT1000 probe
A platinum resistance temperature sensor placed in the liquid, letting a hotplate control the sample temperature rather than the plate temperature.
Heating mantle
A fabric-insulated heater shaped to a round-bottom flask, giving even heating without an open hot surface. See the heating mantle.
Water bath
A heated tank of water that holds samples at a steady temperature for gentle, uniform heating.
pH
pH
A measure of acidity on a 0–14 scale; 7 is neutral, lower is acidic, higher is alkaline. Each unit is a tenfold change in hydrogen-ion activity.
Buffer (calibration buffer)
A solution with a known, stable pH (commonly 4.00, 7.00 and 10.01) used to calibrate a pH meter.
Slope
How much the electrode's mV output changes per pH unit compared with the theoretical value (about 59.16 mV/pH at 25 °C). A slope of roughly 95–105% indicates a healthy electrode.
Offset
The electrode's mV reading in pH 7 buffer, ideally close to 0 mV. A large offset signals a dirty or aging electrode.
ATC (automatic temperature compensation)
Correcting a pH reading for the effect of temperature on the electrode, using a temperature sensor.
Electrode (probe)
The glass sensor that measures pH. Spear-tip electrodes pierce semi-solid foods; general-purpose bulbs suit liquids. Store electrodes wet in storage solution.
2-point / 3-point calibration
Calibrating with two or three buffers that bracket your samples. See how to calibrate a pH meter.
Filtration & glassware
Büchner funnel
A funnel with a flat, perforated or fritted base used with filter paper and vacuum to separate solids from liquids.
Filter (side-arm) flask
A thick-walled flask with a hose barb that connects to vacuum and collects the filtrate.
Frit / porosity
A sintered glass disc with a rated pore size (e.g. 10 µm) that supports filter paper or filters directly. See the vacuum filtration apparatus.
Borosilicate 3.3 glass
Lab glass with low thermal expansion, resistant to heat shock and most chemicals.
Separatory funnel
A tapered funnel with a stopcock used to separate two liquids that don't mix. See how to use a separatory funnel.
PTFE
Polytetrafluoroethylene, a chemically inert plastic used for stopcocks and stir-bar coatings.
Solutions & units
Molarity (M)
Moles of solute per liter of solution. Grams needed = molarity × volume (L) × molecular weight. Use the dilution & molarity calculator.
C1V1 = C2V2
The dilution equation: concentration × volume of the stock equals concentration × volume of the diluted solution.
GSM
Grams per square meter, the standard measure of fabric and paper weight. See the GSM calculator.
Troy ounce (ozt) and pennyweight (dwt)
Precious-metal units: 1 ozt = 31.1035 g; 1 dwt = 1/20 ozt = 1.5552 g. Convert with the weight unit converter.
Carat (ct)
A gemstone weight unit equal to 0.2 g. Not to be confused with karat, a measure of gold purity.
Loss on drying (LOD)
Moisture content found by weighing a sample before and after drying. Moisture analyzers do this automatically. See moisture analyzers.
