Industrial maintenance terms, defined.

A unit of boiler output equal to 33,475 Btu/h, the heat needed to evaporate 34.5 lb of water per hour from and at 212 °F. About 9.81 kW.

Boiler horsepower calculator

The safety control that sequences a burner through purge, ignition, flame proving, run and post-purge, supervises the flame and interlocks, and locks the burner out on a safety failure.

Burner management systems compared

Another name for the burner control that proves flame with a flame detector and shuts off fuel if flame is not proven within the trial time or is lost while firing.

A safety shutdown that needs a manual reset, raised when the burner control detects a failure such as no flame on ignition trial or flame loss during run. The first-out cause should be found before resetting.

Burner lockout vs flame failure

A shutdown after which the burner control restarts the sequence by itself, for example when an operating limit opens and closes again. Unlike a lockout, it needs no manual reset.

The period before ignition when the combustion-air fan clears the furnace of combustible gas, with air flow proven, typically for at least four air changes.

The fixed, short period in which the igniter and pilot or main fuel are energised and the flame detector must prove flame, or the control locks out.

A flame detector that senses the ultraviolet radiation of a flame. Self-checking UV scanners use a shutter to prove the tube has not failed in a flame-present state, which is needed for continuously firing burners.

A flame detector that uses flame rectification: the flame conducts a small DC current between the rod and the burner ground, measured in microamps by the burner control.

A device that shuts the burner off when boiler water falls to an unsafe level. Float and probe types exist; a manual-reset type is often required as the second, safety cutoff.

A burner-control feature that records which interlock or limit opened first, so the root cause is not hidden by the faults that follow it.

Removing boiler water to control dissolved solids (continuous or surface blowdown) or sludge (bottom blowdown).

Boiler blowdown calculator

The ratio of dissolved solids in boiler water to those in feedwater. Higher cycles mean less blowdown but more risk of scale and carryover.

Boiler water droplets or foam leaving with the steam, usually from high water level, high TDS, foaming or sudden load swings. It contaminates the steam system.

The ratio of a burner’s maximum firing rate to its minimum stable firing rate, e.g. 10:1. Higher turndown reduces on/off cycling at low load.

Closed-loop correction of the air/fuel ratio using a flue-gas oxygen analyser, keeping excess air low as fuel, air temperature and load change.

Combustion efficiency calculator

A boiler in which hot combustion gases pass through tubes surrounded by water. Common for packaged boilers up to about 150 psig steam.

Firetube vs watertube boilers

A boiler in which water flows inside tubes heated by the combustion gases outside them. Suited to higher pressures and capacities and faster start-up.

An electronic controller that runs an AC motor at variable speed by converting the supply to DC and inverting it to a variable-frequency, variable-voltage output.

VFD fault troubleshooting

The internal DC voltage stage of a drive, smoothed by capacitors, between the rectifier and the inverter. Its voltage is monitored for over- and undervoltage faults.

A drive trip raised when output current exceeds the hardware or software limit, typically from short ramps, mechanical jams, motor or cable faults, or incorrect motor data.

VFD fault codes by brand

A trip raised when the DC bus voltage rises above its limit, most often from regenerative energy while decelerating a high-inertia load without enough braking capacity.

A trip raised when the drive detects current leaking from its output to earth, pointing at motor or cable insulation, moisture or the drive output stage.

A resistor connected through a brake chopper that burns off regenerative energy as heat, preventing DC bus overvoltage during fast deceleration.

For centrifugal fans and pumps, flow varies with speed, pressure with speed squared and power with speed cubed. They are why VFDs save energy on variable-flow loads.

VFD energy savings calculator

An inductor in the supply to a drive that reduces harmonic current and protects the rectifier from supply transients.

An output filter that slows the voltage rise time of a drive’s pulses, reducing voltage stress on motor insulation over long cable runs.

A drive safety function that removes the energy that produces torque in the motor without removing power from the drive. It must never be bypassed.

A CNC alarm raised by an axis drive or the position loop, for example excess position error, overload or an amplifier not ready. On FANUC controls these carry the SV prefix.

CNC alarm codes by control

An alarm raised when the difference between commanded and actual axis position exceeds a set limit, while stopped or moving. Usually mechanical binding, overload, tuning or feedback.

Moving an axis to its machine reference point so the control knows absolute machine coordinates. Needed after power-up on machines without absolute position detection.

An absolute encoder that keeps axis position through power-off using a backup battery. A flat battery or disconnected cable means position is lost and reference must be re-established.

An alarm raised when an axis reaches a hardware limit switch or a software stroke limit. The axis can usually only be jogged back in the opposite direction.

A display of spindle motor load as a percentage of its rated output. Sustained readings above 100 % can lead to spindle overload or overheating alarms.

Speeds and feeds calculator

The drive that powers a servo motor and closes the current, velocity and often position loops using encoder feedback.

Servo alarm troubleshooting

A servo alarm raised when the amplifier cannot read valid serial data from the motor encoder, most often from cable damage, connector contamination, noise or a failed encoder.

Servo alarm codes by brand

The difference between commanded and actual position of a servo axis while moving. An alarm is raised when it exceeds the configured limit.

Load inertia reflected to the motor shaft divided by the motor rotor inertia. High ratios make a servo axis harder to tune and more prone to resonance.

Servo inertia ratio calculator

A servo drive function that estimates load inertia and sets loop gains automatically, often with notch filters for mechanical resonance.

Energy returned from a decelerating motor to the drive’s DC bus. Too much of it causes an overvoltage alarm unless it is absorbed by a regenerative resistor or returned to the supply.