BOMI SMT cheat sheet

Work is defined as force times distance (W = F × d); power is work divided by time (P = W/t), expressed in watts when work is in joules and time in seconds.

Electrical power in a resistive load follows P = V × I, with V = I × R and P = I²R; these three forms are interchangeable for troubleshooting single-phase circuits.

Sensible heat load for air is Q = 1.08 × cfm × ΔT (°F); for water use Q = 500 × gpm × ΔT. Both constants assume standard density and specific heat.

Total heat (enthalpy) change equals 4.5 × cfm × Δh where Δh is the enthalpy difference in Btu per pound of dry air.

A belt-driven fan delivering less air than design usually indicates slipping or worn belts, incorrect sheave ratio, or restricted return; check amperage against nameplate before adjusting airflow.

Bearing temperature rise above ambient of more than about 40°F (22°C) on a grease-lubricated motor bearing signals over-greasing, misalignment, or impending failure.

Pump cavitation produces a rattling or gravel sound and reduced discharge pressure; root causes are low net positive suction head, a restricted suction strainer, or air ingress.

Vibration analysis decision rule: overall velocity in the 0.5–1.0 in/s RMS band is acceptable for most general-purpose machines; above 0.3 in/s RMS indicates attention per ISO 10816-style bands.

Lockout/tagout sequence: notify occupants, shut down, isolate all energy sources, release stored energy, verify zero energy by test, then apply locks and tags.

Life-cycle cost compares alternatives by summing acquisition, operating, maintenance, and disposal costs discounted to present value; the lowest total wins, not the lowest bid price.

Present value of a recurring annual cost equals the annual amount times the present worth factor; a simple approximation for a single future cost is PV = FV / (1 + i)^n.

Simple payback period in years equals initial investment divided by annual net savings; it ignores time value of money and is used only as a screening metric.

Return on investment equals net annual savings divided by total installed cost, expressed as a percentage; compare against the organization's hurdle rate.

Preventive maintenance compliance is measured as completed scheduled tasks divided by total scheduled tasks for the period, expressed as a percentage.

Mean time between failures equals total operating hours divided by the number of failures; availability equals MTBF divided by (MTBF plus mean time to repair).

A work order system should capture requester, asset ID, priority, labor hours, parts consumed, and completion date; missing any field breaks cost-per-asset reporting.

Inventory reorder point equals average daily usage times lead time in days plus safety stock; safety stock covers demand variability during replenishment.

Capital versus expense classification: an item that extends useful life or increases capacity is capitalized; a like-for-like repair restores function and is expensed.