Digital manometers are useful because they make pressure measurement and transmitter calibration simpler in the field.

Instead of setting up bulky equipment, a technician can use a digital manometer or handheld pressure calibrator with a pressure source, fittings, tubing and the transmitter’s 4–20 mA loop.

The original JM Test article explains a common pressure transmitter calibration setup: the digital manometer is connected through a tee to the pressure transmitter and a pressure source, often a hand pump. The transmitter’s 4–20 mA output is also connected to the digital manometer, and an auxiliary 24 VDC loop supply may be used where needed. 

For Canadian instrumentation teams, this type of setup is common in:

• Oil and gas
• Utilities
• Water and wastewater
• Chemical processing
• Food and beverage
• Manufacturing
• HVAC and building automation
• Power generation
• Pulp and paper
• Mining
• Calibration labs
• Field service work

The goal is simple:

Does the transmitter output match the pressure being applied?

What Is a Digital Manometer?

A digital manometer is an instrument used to measure pressure electronically.

Depending on the model, it may measure:

• Gauge pressure
• Differential pressure
• Absolute pressure
• Vacuum
• Compound pressure
• Low pressure in inches of water column
• Higher pressure in psi, kPa, bar or other units

Some digital manometers are simple pressure indicators.

Others are pressure calibrators that combine pressure measurement with electrical measurement, 4–20 mA reading, voltage/current sourcing, datalogging and loop power support.

The source JM Test article focuses on higher-accuracy digital manometers / calibrators, such as the Meriam M400, used for pressure transmitter calibration, pressure recorder calibration and other pressure measuring devices. 

Why Digital Manometers Are Useful for Pressure Calibration

Digital manometers are useful because they are portable, readable and practical for field work.

They can help with:

• Pressure transmitter calibration
• Pressure recorder checks
• Differential pressure measurement
• HVAC air pressure checks
• Filter differential pressure checks
• Low-pressure process checks
• Leak testing support
• Field troubleshooting
• Verification of pressure switches
• Bench calibration support
• Process loop checks
• Data logging where supported

The original article highlights the speed and simplicity of digital manometer calibration compared with other methods because there are no large boxes, gas cylinders, regulators, weights, special platforms or levelling procedures to manage. 

That does not mean digital manometers replace every pressure standard.

It means they are practical when the instrument range, accuracy, uncertainty, medium compatibility and certificate requirements match the job. 

How a Digital Manometer Is Used to Calibrate a Pressure Transmitter

A basic pressure transmitter calibration setup includes:

• Digital manometer or pressure calibrator
• Pressure transmitter
• Pressure source, such as a hand pump
• Tee fitting
• Tubing or hose
• Correct fittings and adapters
• 4–20 mA loop connection
• 24 VDC loop supply if required
• Calibration record or work order

The typical process is:

1. Connect the digital manometer, transmitter and pressure source through a tee.
2. Connect the transmitter’s 4–20 mA output to the calibrator or current measurement input.
3. Supply 24 VDC loop power if the transmitter requires it.
4. Zero the digital manometer.
5. Apply zero pressure.
6. Verify or adjust the transmitter output to 4 mA.
7. Apply full-scale pressure.
8. Verify or adjust the transmitter output to 20 mA.
9. Check intermediate points if required.
10. Record as-found and as-left results.

The source article describes this same zero-and-span workflow: with zero pressure applied, the transmitter is adjusted for 4 mA; at full-scale pressure, the transmitter output is adjusted for 20 mA. 

Why 4–20 mA Output Matters

Many pressure transmitters use a 4–20 mA output signal.

In a simple linear transmitter:

• 4 mA usually represents the lower range value.
• 20 mA usually represents the upper range value.
• Values between 4 and 20 mA represent pressure across the calibrated range.

For example, a 0 to 100 psi transmitter may be set up so that:

A digital manometer / calibrator helps because the technician can read pressure and mA output together.

That makes the transmitter easier to verify and adjust.

Zero and Span Calibration

Pressure transmitter calibration often starts with zero and span.

Zero

Zero confirms the transmitter output at the low end of the range.

For many transmitters, zero pressure should correspond to 4 mA.

If the transmitter reads 4.08 mA at zero pressure, the loop may be slightly high at the low end.

Span

Span confirms the transmitter output at the high end of the range.

For many transmitters, full-scale pressure should correspond to 20 mA.

If a 0 to 100 psi transmitter reads 19.80 mA at 100 psi, the transmitter may be slightly low at full scale.

The source JM Test article describes this process using a digital manometer, pressure source and transmitter loop, with 4 mA checked at zero and 20 mA checked at full scale. 

Why Multi-Point Calibration Is Better Than Only Zero and Span

Zero and span checks are useful, but they may not catch every problem.

A transmitter may read correctly at 0% and 100% but still have error in the middle of the range.

A better calibration may include points such as:

• 0%
• 25%
• 50%
• 75%
• 100%
• 75% descending
• 50% descending
• 25% descending
• 0% descending

Multi-point checks can help identify:

• Linearity error
• Hysteresis
• Repeatability issues
• Mechanical problems
• Sensor drift
• Incorrect range setup
• Output scaling problems
• Process loop issues

The exact points should come from the procedure, customer requirement, quality system or manufacturer instructions.

Where Digital Manometers Are Used

Pressure Transmitter Calibration

This is the main application in the source article.

A digital manometer can provide the pressure reference while the calibrator reads or verifies the 4–20 mA output. 

Differential Pressure Measurement

Digital manometers are useful for low differential pressure applications such as filters, airflow, HVAC systems, cleanrooms and process equipment.

HVAC and Building Automation

Technicians may use digital manometers to check duct static pressure, pressure switches, filter pressure drop, fan performance and air handling systems.

Water and Wastewater

Digital manometers may be used for process pressure checks, level transmitter work, pump systems, flow-related differential pressure and instrumentation troubleshooting.

Oil and Gas

Pressure transmitters are used across pipelines, tank farms, refineries, gas plants, compressor stations and process units.

Chemical and Process Plants

A digital manometer can support transmitter verification, shutdown work, loop checks and maintenance documentation.

Calibration Labs

Bench technicians may use digital pressure calibrators as part of a controlled calibration process when the instrument and uncertainty are suitable.

Digital Manometer vs Pressure Gauge

A pressure gauge usually gives a direct pressure reading.

A digital manometer may do that too, but many calibrator-style manometers offer more functions.

A digital pressure calibrator may include:

• Pressure measurement
• 4–20 mA measurement
• Voltage measurement
• 24 VDC loop power
• Current sourcing
• Datalogging
• Multiple pressure units
• Differential pressure measurement
• USB or data export
• Field calibration workflow support

The Meriam M400 product information says the M400 includes one pressure sensor and one mA/V instrument, can provide temporary 24 VDC power and measure loop current simultaneously, and can save pressure, VDC and mA values to an SD card for data logging. 

That is why a calibrator-style digital manometer can be more useful than a basic pressure gauge for transmitter work.

Accuracy, Range and Resolution Matter

Not every digital manometer is suitable for every calibration job.

Before using one, confirm:

• Pressure range
• Pressure type
• Accuracy
• Resolution
• Measurement uncertainty
• Units
• Temperature effect
• Media compatibility
• Pressure connection
• Overpressure rating
• Electrical measurement accuracy
• Current calibration status
• Certificate type
• Traceability
• Accredited scope if required

The original article says a calibrator-class digital manometer may indicate pressure to 0.05% of reading, while a good hand pump may set pressure to a fine resolution such as 0.01 inH₂O. 

Meriam M4 Series product information also lists model-dependent pressure and electrical accuracy specifications, so the exact M400 or M402 configuration should always be checked before use. 

Pressure Range Selection

A digital manometer should be selected for the pressure range being calibrated.

If the range is too high, the reading may not have enough resolution for low-pressure work.

If the range is too low, the instrument may be damaged or overloaded.

For example:

• A low-pressure HVAC transmitter may need a manometer in inches of water column or pascals.
• A process transmitter may need psi, kPa or bar.
• A differential pressure transmitter may need a differential sensor, not a single-port gauge sensor.
• A compound transmitter may need both vacuum and positive pressure coverage.
• An absolute pressure transmitter needs an absolute pressure reference.

Do not choose the instrument only by convenience.

Choose it based on the transmitter range, tolerance and required uncertainty.

Media Compatibility Matters

Pressure calibrators and digital manometers are not all compatible with the same media.

Some sensors are designed for clean, dry, non-corrosive gas.

Others use isolated stainless-steel sensors suitable for liquids or broader process media.

Before connecting a digital manometer, confirm:

• Gas or liquid service
• Cleanliness of the process
• Corrosive media risk
• Oil or water contamination
• Sensor isolation
• Wetted materials
• Pressure connection
• Need for isolation valves
• Need for flushing or cleaning
• Decontamination requirement before service

This is especially important when calibrating instruments removed from chemical, oil and gas, wastewater or food processing systems.

Loop Power and mA Measurement

Some transmitter loops already have loop power.

Others need temporary 24 VDC power during bench or field calibration.

The source article notes that an auxiliary loop supply may provide 24 VDC power if needed. 

Many pressure calibrators simplify this by providing loop power and mA measurement in the same handheld unit.

The Meriam M400 product information says the instrument can provide temporary 24 VDC power and measure loop current simultaneously, depending on the model and setup. 

This reduces the number of tools needed at the jobsite.

Datalogging and Documentation

Datalogging can be helpful when calibration or troubleshooting requires recorded evidence.

It can support:

• Calibration records
• Loop checks
• Trend review
• Shutdown documentation
• Troubleshooting reports
• Customer acceptance
• Audit support
• As-found / as-left comparison

Meriam M400 product information says pressure, VDC and mA DC values can be saved to an SD card at each interval for M400 single-pressure-sensor units. 

Datalogging does not replace a calibration certificate, but it can support better records.

As-Found and As-Left Results

A useful calibration should show how the transmitter performed before and after adjustment.

As-Found

As-found data shows the condition of the transmitter before adjustment.

This helps answer:

• Was the transmitter within tolerance while it was in service?
• Were recent process readings reliable?
• Should any process data be reviewed?
• Should the calibration interval be shortened?

As-Left

As-left data shows the transmitter after adjustment or final verification.

This helps confirm whether the transmitter is ready to return to service.

JM Test Canada’s calibration services page states that calibration documentation includes as-found and as-left data, traceable certificates, calibration stickers and electronic records through its customer portal. 

Canadian Calibration and Traceability Context

For Canadian calibration work, traceability should be documented, not assumed.

NRC Canada’s Metrology Research Centre is Canada’s national metrology institute and provides accurate, traceable measurements that define Canada’s national standard. 

ISO/IEC 17025 is the international standard for testing and calibration laboratories, covering competence, impartiality and consistent operation. 

NRC states that its Calibration Laboratory Assessment Service was discontinued effective April 30, 2026, and that SCC is now fully responsible for assessment and accreditation to ISO/IEC 17025 for those testing and calibration laboratories. 

For pressure transmitter calibration, confirm:

• Traceability chain
• Calibration certificate type
• Standards used
• Measurement uncertainty
• Pressure range covered
• Electrical measurement range covered
• Whether ISO/IEC 17025 accredited calibration is required
• Whether the provider’s scope includes the required pressure range and method

Field Calibration vs Lab Calibration

Field Calibration

Field calibration is useful when the transmitter is installed or when downtime must be minimized.

It can help with:

• Fast checks
• Loop verification
• Shutdown work
• Commissioning
• Troubleshooting
• Onsite adjustments
• Reducing instrument removal

Lab Calibration

Lab calibration may be better when:

• Higher accuracy is required
• Better environmental control is needed
• The instrument needs repair
• Accredited calibration is required
• The transmitter must be tested across multiple points
• The customer requires a specific certificate format
• Better pressure standards are needed

JM Test Canada says it provides onsite and mobile calibration lab services, and its calibration services page lists pressure / vacuum / test equipment services including gauges, pneumatic calibrators, hand pumps, manometers, digital pressure indicators / calibrators, pressure switches and pressure transmitters / transducers. 

Common Mistakes During Pressure Transmitter Calibration

Not Zeroing the Digital Manometer

The source article starts the procedure by zeroing the digital manometer before applying pressure. 

Skipping this step can create avoidable error.

Using the Wrong Range

A high-range instrument may not give enough resolution for low-pressure work.

Ignoring Loop Power

If the transmitter needs loop power and none is supplied, the output cannot be checked correctly.

Checking Only 4 mA and 20 mA

Zero and span are useful, but they do not always prove linearity across the range.

Using the Wrong Pressure Medium

Some sensors are meant only for clean dry gas. Others can handle liquids. Confirm compatibility first.

Ignoring Units

Pressure may be shown in psi, kPa, bar, mbar, inH₂O, cmH₂O or Pa.

Make sure the transmitter, procedure and calibrator are using the correct units.

Not Recording As-Found Data

If the transmitter was out of tolerance, as-found data may help decide whether past readings should be reviewed.

Assuming Every Calibration Is Accredited

Accreditation depends on the lab’s current scope, method, range and uncertainty.

Forgetting the Hand Pump and Fittings

A good calibrator still needs the right pressure source, hose, tee, fittings and adapters.

What to Confirm Before Renting or Buying a Digital Manometer

Before choosing a digital manometer or pressure calibrator, confirm:

• Pressure range
• Gauge, absolute, differential or compound pressure
• Required accuracy
• Required resolution
• Required units
• Media compatibility
• Pressure connection
• Overpressure rating
• mA measurement requirement
• 24 VDC loop power requirement
• HART resistor requirement if applicable
• Datalogging requirement
• Calibration certificate requirement
• ISO/IEC 17025 requirement
• Hand pump requirement
• Tubing and fitting kit
• Field or lab use
• Battery life
• Environmental conditions
• Canadian availability
• Rental or purchase option

JM Test Canada’s rental page says its rental division includes instrument and controls, electrical, communications, gas detection, utility products and mechanical equipment. 

For pressure transmitter work, confirm the exact digital manometer, hand pump, fittings, certificate and accessories before booking.

Canadian Industries That Use Digital Manometers

Oil and Gas

Pressure transmitters are used across wells, pipelines, refineries, tank farms, compressor stations and gas plants.

Water and Wastewater

Digital manometers help verify pressure and differential pressure instrumentation across pumps, filters, level systems and process lines.

HVAC and Building Automation

Low-pressure digital manometers are common for duct static pressure, filter pressure drop and air handling system work.

Manufacturing

Manufacturing plants use pressure transmitters for process control, hydraulic systems, pneumatic systems and quality checks.

Power Generation

Transmitters are used across steam, water, air, fuel, hydraulic and auxiliary systems.

Food and Beverage

Calibration supports process consistency, sanitation controls and quality records where pressure measurements are part of the process.

Laboratories and Calibration Shops

Digital pressure calibrators support bench work, field instrument checks and customer documentation.

JM Test Systems Canada Support

JM Test Canada lists pressure / vacuum / test equipment calibration services that include:

• Gauges
• Pneumatic calibrators
• Hand pumps
• Vacuum pumps
• Manometers
• Deadweight tester calibration
• Digital pressure indicators / calibrators
• Pressure switch calibration
• Pressure transmitters / transducers
• Pneumatic controllers 

Its calibration services page also describes onsite and mobile calibration lab services, traceable certificates, customer portal access, calibration stickers, QR-coded certificates and as-found/as-left data. 

For the Canadian page, avoid copying the US page’s Baton Rouge contact details or US-only Meriam rental language directly. Confirm Canadian availability, certificate type, accessories and service scope before publishing firm claims.

Practical Takeaway

Digital manometers are useful tools for pressure transmitter calibration because they can combine pressure measurement, 4–20 mA loop verification and field portability.

The source JM Test article shows a simple calibration setup: connect the digital manometer, transmitter and pressure source through a tee, read the transmitter’s 4–20 mA output, zero the manometer, check 4 mA at zero pressure and check 20 mA at full-scale pressure. 

For Canadian teams, the key is to match the instrument to the job.

Confirm the pressure range, accuracy, units, media compatibility, loop power needs, calibration certificate, uncertainty, traceability and accessories before using or renting the equipment.

JM Test Systems Canada can support pressure, vacuum, manometer, digital pressure calibrator and pressure transmitter calibration needs where available. Confirm the exact model, range, certificate type, ISO/IEC 17025 scope, fittings, hand pump, rental terms and Canadian service details before booking.