Extech Pressure Meters & Digital Manometers

A digital manometer measures the difference in pressure between two points, or between one point and the surrounding atmosphere, using a silicon sensing element in place of the liquid column that gave the instrument its name. Extech's pressure range spans 0.5 psi to 101.5 psi (34 mbar to 7000 mbar) in eight current models, from high-resolution low-range meters for cleanroom and duct work through to SD-card dataloggers for unattended compressed-air and hydraulic monitoring.

Ecotao Enterprises supplies the Extech pressure range from our Cape Town base to customers throughout South Africa, Namibia, Botswana, Zimbabwe, Mozambique, Lesotho and Eswatini. This page sets out what each model actually measures, how the ranges differ in practice, and how to size an instrument so you are not spending most of your accuracy budget on span you will never use.

Extech pressure meter range at a glance

All eight models are two-port instruments, so each can work as a differential meter using both ports or as a gauge meter with one port open to atmosphere. The split that matters is between handheld meters with a live PC interface and SD-card dataloggers that can be left running unattended.

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Discontinued: Extech SDL700 and PT-series transducers

How to choose the right pressure meter range

Sizing a manometer is a three-step decision. Work through it in this order, because the first step eliminates most of the catalogue and the third one is the only place where budget should enter.

Step 1 — Establish your expected maximum, then add about 25%

Take the highest pressure you realistically need to read, not the highest the system could theoretically reach. A typical commercial HVAC filter bank runs 50–250 Pa clean and is changed somewhere around 500–750 Pa, which is 0.007 to 0.11 psi — a job for the HD755 at 0.5 psi. A shop compressed-air ring at 6 bar is 87 psi, which needs the SDL730 at 101.5 psi. A side-channel blower discharging at 250 mbar is 3.6 psi, which lands on the HD750 at 5 psi. Adding roughly 25% headroom protects the sensor against transients without pushing you into a range that costs you resolution.

Step 2 — Decide whether you need a record or just a reading

If a technician stands at the instrument, reads a number, writes it on a commissioning sheet and moves on, a handheld HD-series meter is the right tool: it powers up instantly, resolves finely, and the USB interface is there when a live trace is occasionally useful. If the question is "what is this system doing at 03:00 on a Sunday", no amount of resolution helps and you need an SDL-series logger writing to an SD card. Filter loading trends, compressor duty cycling, intermittent pressure drops and night-setback verification all fall into the second category, and all of them are effectively invisible to spot readings.

Step 3 — Check whether pressure is actually what you want

A surprising share of pressure-meter enquiries are really airflow enquiries. If the deliverable is m³/h, CFM or m/s rather than pascal, the HD350 does the conversion internally from a pitot tube differential and saves a manual calculation on every reading. Buying a pure manometer and a separate pitot tube works, but you will be applying the velocity-pressure equation by hand at every traverse point, which is where duct traverse errors usually creep in.

The Extech pressure meter range

Eight current models, listed from lowest range to highest. Handheld meters first, then the SD-card datalogger family.

Handheld · Lowest range

Extech HD755

Differential Pressure Manometer — 0.5 psi

The finest-resolution instrument in the range. At 0.001 psi resolution across a 0.5 psi span, the HD755 reads the small differentials that make up most building-services work — the pressure drop across a filter bank, the cascade between a cleanroom and its anteroom, the static in a low-velocity supply duct. Those readings sit in the bottom 2% of a 29 psi meter's scale and are effectively unmeasurable on one. The zero function corrects for sensor offset before each set of readings, and the built-in USB port streams a live trace when you need to watch a value settle rather than catch it once.

• Range0 to 0.5 psi / 13.85 inH₂O
• Resolution0.001 psi
• Accuracy±0.3% full scale
• Units11 selectable
• InterfaceUSB (software + cable)

Right choice when: your readings are in pascal rather than bar — cleanroom pressurisation, filter differential, fume cupboard face pressure, low duct static.

Enquire about the HD755

Handheld · Airflow

Extech HD350

Pitot Tube Anemometer + Differential Manometer

A differential manometer that finishes the calculation for you. Feed it velocity pressure from the supplied pitot tube and it displays air velocity and volumetric flow alongside the raw pressure and temperature, on one screen, in the units your specification is written in. That matters most on a duct traverse, where a technician takes readings at a dozen points across a cross-section: doing the velocity-pressure conversion by hand at every point is where traverse errors normally come from. The pitot tube and its two 85 cm hoses reach into ducts and plenums that a vane anemometer cannot enter, and the 99-reading store means a full traverse can be captured before anything is written down.

• Pressure range±0.7252 psi (50 mbar)
• Air velocity200 to 15733 ft/min
•  3.5 to 288.0 km/h
• Accuracy±1% full scale
• Units5 pressure units
• Memory99 readings per mode
• InterfaceUSB (software + cable)

Right choice when: the deliverable is m³/h, CFM or m/s rather than pascal — duct traverses, extraction system commissioning, fan performance verification.

Enquire about the HD350

Handheld · New to this page

Extech HD700

Differential Pressure Manometer — 2 psi

The general-purpose middle of the HD family, and the model most HVAC contractors end up carrying. Two psi is 55.40 inches of water column, which comfortably covers fan discharge static, ducted system total pressure and a heavily loaded filter bank without the resolution penalty of jumping to a 5 psi or 29 psi range. Accuracy holds at ±0.3% full scale across the span, and the relative time stamp on Max/Min recording tells you not just what the extremes were but when they occurred — useful when a system is cycling and you are trying to correlate a pressure spike with a damper movement. Supplied with an AC adaptor as well as a 9V battery, so it can sit powered on a bench for extended tests.

• Range0 to 2 psi / 55.40 inH₂O
• Equivalent0.137 bar
• Accuracy±0.3% full scale
• Units11 selectable
• RecordingMax/Min + relative time stamp
• InterfaceUSB (software + cable)

Right choice when: you want one meter that handles most building-services pressure work — fan static, ducted total pressure, loaded filters, balancing dampers.

Enquire about the HD700

Handheld · New to this page

Extech HD750

Differential Pressure Manometer — 5 psi

Five psi — 344 mbar, or 138.3 inches of water column — is the natural range for equipment that sits between HVAC and true pneumatics. Side-channel and regenerative blowers, aeration diffuser headers in wastewater and aquaculture, gas train pressure ahead of a burner, and dust extraction plant with heavily loaded bag filters all live here. Below this range a 2 psi meter over-ranges; above it a 29 psi meter throws away most of its resolution. The HD750 shares the HD-family ±0.3% full-scale accuracy, 11 selectable units and USB interface, so a fleet of HD700, HD750 and HD755 meters behaves identically in the hand and produces interchangeable data files.

• Range0 to 5 psi / 138.3 inH₂O
• Equivalent0.344 bar
• Accuracy±0.3% full scale
• Units11 selectable
• RecordingMax/Min + relative time stamp
• InterfaceUSB (software + cable)

Right choice when: you are measuring blower discharge, aeration header pressure or gas train pressure — too high for a 2 psi meter, too low to waste on a 29 psi one.

Enquire about the HD750

Handheld · Heavy duty

Extech 407910

Heavy Duty Differential Pressure Manometer — 29 psi

The rugged member of the range, built for pneumatic and compressed-air work where the instrument gets carried around a plant rather than kept in a case. Twenty-nine psi is 2 bar, which covers shop air lines, pneumatic cylinder supply pressure, air-operated valve actuators and the discharge side of small compressors. The two quick-disconnect fittings matter more than the specification sheet suggests: on pneumatic circuits you are constantly moving between test points, and threaded connections slow that down considerably. A protective holster with an integral stand lets the meter be propped against plant while both hands are on a spanner, and the RS-232 interface with supplied software captures a trace when a fault is intermittent.

• Range±29 psi (2 bar)
• Resolution0.02 psi
• Accuracy±1% full scale
• Units8 selectable
• Fittings2 × quick-disconnect
• InterfaceRS-232 (software included)

Right choice when: the work is pneumatic and mobile — shop air, cylinder supply, actuator pressure, small compressor discharge, general plant maintenance.

Enquire about the 407910

Datalogger · New to this page

Extech SDL710

Differential Pressure Manometer / Datalogger — 2.9 psi

The low-range member of the SDL logging family, covering 200 mbar with dual differential inputs and internal sensors. Its reason for existing is unattended measurement: a filter bank that loads gradually over three weeks, a cleanroom cascade that drifts only when a particular door is used, a night-setback sequence that nobody is on site to watch. The SD card writes directly in Excel-compatible format, so there is no proprietary export step — pull the card, open the file, plot the trend. Ninety-nine readings can also be stored manually for conventional spot checks, which means one instrument covers both survey work and long-term logging.

• Range2.9 psi (200 mbar / 200 hPa)
• Equivalent80.2 inH₂O / 0.197 atm
• Accuracy±2% full scale
• InputsDual differential, internal sensors
• LoggingSD card, Excel format
• Manual store99 readings

Right choice when: the answer requires a trend, not a number, and the pressures are low — filter loading studies, cleanroom cascade verification, ventilation performance over a full duty cycle.

Enquire about the SDL710

Datalogger · SDL700 replacement

Extech SDL720

Differential Pressure Manometer / Datalogger — 29 psi

The mid-range logger, and the natural upgrade path for anyone previously running an SDL700 with a 30 psi transducer. Twenty-nine psi (2000 mbar) covers compressed-air reticulation, process gas headers and the pressure side of most industrial blower installations. The design change worth understanding is that the sensing elements are now inside the meter as dual differential inputs, rather than plugged in as separate transducers — one fewer item to specify, calibrate, match to a range, or lose on site. Everything else behaves as before: SD card logging in Excel format, 99 manual stores, and a dual display that shows both channels at once.

• Range29 psi (2000 mbar / 2000 hPa)
• Equivalent802 inH₂O / 1.974 atm
• Accuracy±2% full scale
• InputsDual differential, internal sensors
• LoggingSD card, Excel format
• Manual store99 readings

Right choice when: you are logging compressed air or process gas, or replacing a discontinued SDL700 with a 30 psi PT30 transducer.

Enquire about the SDL720

Datalogger · Highest range

Extech SDL730

Differential Pressure Manometer / Datalogger — 101.5 psi

At 101.5 psi (7000 mbar) this is the highest range in the Extech pressure family and the only model that reaches into hydraulic territory. Typical work is compressed-air ring main surveys at 6–7 bar, pump discharge testing, hydraulic circuit monitoring and any application where a system is expected to hold pressure over time and the question is whether it actually does. Because it logs continuously to SD card, it answers leak-down and duty-cycle questions that a spot reading cannot: a compressed-air ring that reads 6.2 bar at 09:00 on a Tuesday tells you almost nothing about what happens during a shift change.

• Range101.5 psi (7000 mbar / 7000 hPa)
• Equivalent2810 inH₂O / 6.905 atm
• Accuracy±2% full scale
• InputsDual differential, internal sensors
• LoggingSD card, Excel format
• Manual store99 readings

Right choice when: pressures run to several bar and the question is about behaviour over time — compressed-air leak-down surveys, pump testing, hydraulic circuit monitoring.

Enquire about the SDL730

Gauge, differential and absolute pressure explained

These three terms describe what the reading is measured against, and confusing them is the most common source of pressure measurement errors. Every Extech meter on this page reads gauge and differential; absolute pressure requires a barometer or a dedicated absolute transducer.

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Where these instruments earn their keep

HVAC commissioning and building services

Commissioning an air handling system means proving that design airflow is actually reaching each terminal, and pressure is how that gets established. Duct static readings identify where a system is losing pressure it should not be; filter differentials establish clean baseline values that later become change-out triggers; fan total pressure confirms the unit is operating on the part of its curve the designer intended. These readings are small — typically 25 to 750 Pa — which is exactly why range selection matters here more than in any other application. An HD755 or HD700 gives a technician a number they can defend on a commissioning sheet; a 29 psi meter gives them a number sitting inside its own error band.

Cleanroom and containment pressure cascade

Cleanrooms, pharmaceutical suites, laboratory containment areas and hospital isolation rooms rely on maintaining a specified pressure difference between adjacent spaces, so that air always moves in the intended direction. The differentials involved are very low, often 5 to 15 Pa, and they must be demonstrated rather than assumed during validation. The HD755's 0.001 psi resolution is what makes this measurable at all; the SDL710 extends it into continuous verification, which is what auditors increasingly want to see rather than a single witnessed reading.

Compressed air systems and pneumatics

Compressed air is generally the most expensive utility in a plant per unit of delivered work, and most systems lose a substantial share of it to leaks and to pressure drop across undersized reticulation. Establishing where that loss occurs means measuring pressure at several points along a ring and, critically, over time rather than once. The SDL730 logging at 101.5 psi captures overnight leak-down, which is the cleanest way to quantify total system leakage: with no production running, any pressure the system loses is a leak. For hands-on fault finding at individual machines, the 407910's quick-disconnect fittings make moving between test points fast enough to be practical.

Blowers, aeration and wastewater treatment

Aeration is typically the largest electrical load on a wastewater works, and blower discharge pressure is the number that tells you whether that energy is doing useful work. Rising header pressure at constant airflow usually means diffuser fouling; falling pressure can mean a membrane failure or a leaking header. Both are gradual, both are expensive, and both are invisible to occasional spot readings. The HD750 at 5 psi covers most diffused-aeration header pressures directly, and the SDL720 logs the same range continuously so the trend, rather than a single value, drives the maintenance decision.

Dust extraction and filtration plant

Bag houses, cartridge filters and cyclone systems are all managed by differential pressure. Too low a differential can mean a torn bag passing dust straight through; too high means restricted airflow and reduced capture velocity at the hood, which is where an extraction system stops protecting the operator. Continuous logging with an SDL710 across a cleaning cycle shows whether reverse-pulse cleaning is actually restoring the filter or merely delaying a change-out.

Pressure measurement in South African conditions

Altitude, and when it actually matters

South Africa spans a wide altitude range, and this affects pressure work in a way that is often either ignored or over-applied. The rule is straightforward: differential readings need no altitude correction, because both measurement points sit in the same ambient air and the atmospheric component cancels out. A 200 Pa filter differential reads 200 Pa in Cape Town and 200 Pa in Johannesburg. Absolute conversions and any density or mass-flow calculation derived from a pressure reading do need correction, and the difference is large.

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The practical consequence is that a fan or blower performance curve published at sea level overstates delivered mass flow on the Highveld by roughly 17%. Equipment sized from a catalogue curve without altitude derating will underperform, and the symptom usually shows up as a pressure reading that does not match the design figure. Measuring inlet pressure rather than assuming it is the cheapest way to catch this before commissioning.

Units on South African sites

Three unit conventions coexist on most South African plants, which is the main reason a multi-unit instrument is worth having. Building services specifications are written in pascal and kilopascal under SANS conventions. Compressed air and pneumatics are almost always discussed in bar. Imported American equipment — a substantial share of process and HVAC plant — carries documentation in psi and inches of water column. An instrument that switches between all of these in the field removes an entire category of conversion error from the measurement chain, which is why the 11-unit HD-series meters tend to end up being the ones that stay in the toolbox.

Supply and support

Ecotao supplies the Extech pressure range from Cape Town to customers across South Africa, Namibia, Botswana, Zimbabwe, Mozambique, Lesotho and Eswatini. If you are unsure which range suits an application, send us the expected working pressure and what the reading is for — range selection is where most of the value in this decision sits, and it is a five-minute conversation.

Frequently asked questions