When a buyer requests an electromagnet or Helmholtz coil, one question should be answered before the quotation is finalized:
Are you buying a magnet, or are you buying a complete magnetic field system that can generate, measure, verify, and document the field you actually need?
Those are not the same purchase.
A magnet may generate the required field perfectly well. But once the project requires field verification, closed-loop control, uniformity validation, installation acceptance, or repeatable calibration, the delivery scope can expand to include:
- Power supply
- Gaussmeter
- Magnetic field probe
- Probe fixture
- Positioning or field mapping kit
- Control software
- Field calibration data
- Uniformity mapping
- Acceptance documentation
For research institutes, universities, integrators, and tender buyers, defining this boundary early can prevent one of the most common procurement disputes:
“We thought that was included.”
This article explains where buyers should draw the line between a magnet-only purchase and a complete magnetic field system.
1. Start with the Real Question: What Result Must Be Delivered?
A purchase specification should not begin with the equipment list.
It should begin with the expected result.
There is a major difference between these requirements:
Requirement A
“We need an electromagnet capable of producing approximately 1 T.”
and:
Requirement B
“We need a controllable magnetic field of 0–1 T, verified at the sample position, with defined field uniformity over a 20 × 20 × 10 mm working volume and documented acceptance data.”
Requirement A may require a magnet and suitable power source.
Requirement B is already describing a measurement system.
Ask what the laboratory must be able to do after installation
Does the user only need to:
- Generate a magnetic field?
Or must they also:
- Know the actual field?
- Control the field rather than only the current?
- Verify field uniformity?
- Reproduce a field later?
- Calibrate sensors?
- Produce test reports?
- Demonstrate compliance during acceptance?
- Map the complete working volume?
The answer determines the correct delivery scope.
2. A Magnet Is Not Automatically a Complete Magnetic Field System
The word “magnet” can hide several missing components.
Consider an electromagnet.
The magnet itself contains:
- Magnetic yoke
- Pole pieces
- Excitation coils
- Cooling structure where required
But it normally does not generate a controllable field by itself.
It needs an excitation source.
So even before discussing field measurement, buyers should distinguish between:
Magnet Only
Typically:
- Electromagnet or coil assembly
- Mechanical structure
- Basic connection interface
Magnet + Power Supply
Adds:
- Matched current or voltage source
- Polarity control where applicable
- Current adjustment
- Protection functions
- Possible remote interface
Complete Magnetic Field System
May further add:
- Gaussmeter
- Hall probe
- Magnetic feedback
- Software control
- Fixtures
- Mapping capability
- Verification data
- Acceptance documentation
Cryomagtech, for example, distinguishes individual electromagnets from integrated electromagnet-based field generation systems that combine the magnet, excitation power supply, gaussmeter, and control functions. Cryomagtech
This distinction should also appear clearly in the buyer’s RFQ.
3. Level 1: When “Magnet Only” Is Enough
Buying only the magnet can be perfectly reasonable.
It is not automatically an incomplete purchase.
Magnet-only procurement makes sense when the buyer already has:
- Compatible bipolar power supply
- Appropriate cables and connectors
- Cooling infrastructure
- Gaussmeter and probe
- Control electronics
- Existing fixture
- Internal field mapping capability
- Experienced integration engineers
For example, a physics laboratory may already operate several magnetic measurement systems and only need another electromagnet with a particular pole gap.
In that case, paying for duplicate instrumentation would make little sense.
But compatibility must still be checked
A buyer supplying their own power source should confirm:
- Maximum current
- Required voltage
- Coil resistance
- Inductance
- Bipolar or unipolar operation
- Current stability
- Protection strategy
- Cooling requirements
- Cable specification
A power supply that can produce the required current on paper is not automatically suitable for an inductive magnet load.
4. Level 2: Magnet + Power Supply Is the Minimum Practical Field Generator
For many research projects, the more sensible minimum scope is:
Magnet + matched excitation power supply
Now the buyer has a functioning magnetic field generator.
What this package can usually do
It can:
- Energize the magnet
- Adjust the excitation current
- Reverse polarity if a bipolar supply is used
- Sweep current
- Maintain reasonably stable excitation
- Generate repeatable current settings
But there is an important limitation:
Current is not the same thing as measured magnetic field.
If the software commands 10 A, that tells you the electrical excitation.
It does not independently confirm the actual magnetic flux density at the sample.
5. Why Current Control Alone May Not Be Enough
For many magnets and coils, magnetic field is strongly related to current.
For a Helmholtz coil operating in its linear range, the relationship can often be approximated as:
B = K × I
where:
- B = magnetic flux density
- K = coil constant
- I = excitation current
For an electromagnet, the relationship may become more complicated because of:
- Magnetic saturation
- Pole gap
- Pole geometry
- Magnetic hysteresis
- Residual field
- Temperature
- Magnetic material properties
So a current setting is not always an adequate substitute for a measured field value.
The buyer should therefore ask:
Do I need to control current, or do I need to know magnetic field?
That question often determines whether a probe belongs in the delivery scope.
6. Level 3: Add a Gaussmeter and Probe When the Field Itself Matters
Once magnetic field becomes the measured or controlled variable, a field measurement instrument becomes much more important.
A typical package may include:
- Gaussmeter
- Axial or transverse Hall probe
- Probe cable
- Probe holder
- Calibration information
This enables direct field verification
Instead of recording:
Current = 15 A
the laboratory can record:
Magnetic field at reference position = 0.785 T
That difference matters in:
- Hall effect testing
- Magnetoresistance measurements
- MOKE experiments
- Magnetometer calibration
- Magnetic sensor testing
- Material characterization
- Field-dependent spectroscopy
- Device qualification
7. The Probe Should Be Treated as a Measurement Instrument, Not an Accessory
A field probe may look like a small accessory.
Metrologically, it can be one of the most important components in the system.
Probe selection should consider
- Measurement range
- Accuracy
- Resolution
- Axis configuration
- Active area
- Probe thickness
- Temperature sensitivity
- Positioning repeatability
- Calibration status
For narrow electromagnet gaps, probe geometry can become especially important.
A thick probe may physically fit between the poles but place the sensing element away from the intended sample position.
Probe orientation matters too
A single-axis Hall probe measures one field component.
If it is tilted relative to the intended magnetic axis, the measured value can differ from the true axial field.
Therefore, a complete delivery should consider not only the probe itself but also how the probe will be positioned.
8. Calibration and Traceability Are Not the Same as Owning a Probe
This distinction is important in serious research and industrial calibration projects.
A laboratory should not assume that simply owning a calibrated instrument automatically makes every future measurement traceable.
NIST defines metrological traceability through a documented, unbroken chain of calibrations, with each calibration contributing to the measurement uncertainty. NIST also emphasizes that the measurement system and the way values are transferred must be understood and controlled. NIST
This has an important purchasing implication.
If your tender requires:
“traceable magnetic field measurement,”
you should clarify:
- Which instrument is calibrated?
- What calibration documentation is required?
- What measurement uncertainty is acceptable?
- What field range is covered?
- Which probe is associated with that calibration?
- How will the probe be positioned during verification?
“Gaussmeter included” is not a complete metrology specification.
9. Level 4: When You Need a Field Mapping Kit
A single field measurement answers:
What is the magnetic field at this point?
Field mapping answers:
How does the magnetic field change throughout the working region?
Those are very different questions.
A field mapping kit may include
- Calibrated magnetic field probe
- Gaussmeter
- Probe positioning fixture
- Linear translation stage
- XYZ positioning stage
- Rotation mechanism where required
- Position scales or encoders
- Mapping software
- Data acquisition interface
- Coordinate definition
- Mapping procedure
The exact configuration depends heavily on the application.
10. When a Single Center-Field Measurement Is Enough
Not every buyer needs a full mapping system.
If the application only requires a known field at one fixed point, then a center-field measurement may be sufficient.
For example:
- Small sample
- Fixed sample position
- Previously characterized magnet
- Loose uniformity requirements
- Routine field generation
- Non-metrological experiment
A probe permanently mounted at the field center may be enough.
Do not buy complexity without a reason
A motorized three-axis mapping system can add:
- Cost
- Mechanical complexity
- Software integration
- Calibration requirements
- Maintenance
- Setup time
If your experiment does not need spatial field information, it may provide little practical benefit.
11. When Field Mapping Becomes Necessary
Field mapping becomes much more valuable when the specification includes statements such as:
- ±1% uniformity over 50 × 50 × 50 mm
- Field gradient below a defined limit
- Homogeneous field over the entire sample
- Sensor calibration throughout a defined volume
- Vector-field accuracy within a 3D region
Why?
Because field uniformity is not a property of one point.
Example
Suppose an electromagnet produces:
1.000 T at the center
That tells you nothing by itself about whether the field is:
- 0.999 T 10 mm away
- 0.980 T 10 mm away
- 0.900 T 10 mm away
To validate uniformity, measurements must be taken over a defined spatial region.
That is field mapping.
12. Field Uniformity Must Always Be Connected to a Volume
Statements such as:
“Field uniformity: 1%”
are incomplete unless they also define:
- Field level
- Spatial region
- Coordinate system
- Measurement method
- Reference point
- Calculation method
A useful specification might instead say:
Field variation ≤ ±1% relative to the center value within a 20 × 20 × 20 mm³ working volume at 0.5 T.
Now both buyer and supplier know what must be verified.
This is one reason the mapping method should sometimes be part of the delivery specification rather than something discussed after manufacturing.
13. Electromagnets and Helmholtz Coils Need Different Mapping Strategies
Although both generate magnetic fields, their useful field geometries are different.
Electromagnet
An electromagnet commonly concentrates field between pole faces.
Mapping may focus on:
- Axial field
- Pole-gap center
- Horizontal uniformity
- Vertical uniformity
- Sample plane
- Different pole gaps
- Different excitation currents
Helmholtz Coil
A Helmholtz coil is typically selected to generate a relatively uniform field over an open volume.
Mapping may focus on:
- Central uniform region
- X/Y/Z coordinates
- Coil constant
- Axis orthogonality
- Cross-axis coupling
- Vector field accuracy
Cryomagtech’s Helmholtz coil portfolio includes single-, dual-, and three-axis configurations, and complete Helmholtz coil systems can combine the coil set, programmable field measurement, power electronics, and software control. Cryomagtech
Suggested target: Cryomagtech Magnet & Field Systems / Magnetic Field Generation product category. Cryomagtech
14. Do Buyers Need the Mapping Hardware or Only the Mapping Report?
This is a crucial scope question.
There are actually two different requirements.
Option A: Supplier Performs Factory Mapping
The supplier performs the mapping and provides:
- Mapping conditions
- Measurement points
- Field data
- Uniformity calculation
- Field curves
- Test report
The mapping equipment itself is not delivered.
This may be enough when the buyer only needs factory acceptance evidence.
Option B: Mapping Capability Is Delivered to the Customer
The customer receives:
- Probe
- Gaussmeter
- Positioning system
- Fixtures
- Mapping procedure
- Software
- Data acquisition capability
Now the laboratory can repeat the field map after:
- Installation
- Relocation
- Maintenance
- Magnet modification
- Fixture change
These are very different commercial scopes.
A tender that simply says:
“Field mapping required”
does not tell suppliers which one is expected.
15. Factory Mapping and On-Site Mapping Are Also Different
Even if the supplier provides excellent factory field mapping data, the field environment can change after installation.
Possible influences include:
- Steel optical tables
- Magnetic fixtures
- Nearby motors
- Building structure
- Magnetic shielding
- Cables carrying large currents
- Other magnets
- Sensor mounting hardware
This is particularly relevant for low-field Helmholtz coil systems.
Therefore ask:
Do we need to know:
How the system performed at the factory?
or:
How the installed system performs in our laboratory?
If the second question matters, the customer may need either:
- Delivered mapping capability, or
- On-site commissioning and mapping
16. Closed-Loop Field Control Changes the System Boundary Again
There is another major difference between:
measuring the field
and:
using the measured field as feedback to control the field.
Open-loop control
The system commands current:
I_target → Power Supply → Magnet
Field is inferred from current or previously measured calibration data.
Closed-loop field control
The system may operate more like:
B_target → Controller → Power Supply → Magnet → Field Probe → Feedback
Now the gaussmeter and probe are part of the actual control architecture.
They are no longer optional verification tools.
Cryomagtech’s Helmholtz coil systems can be configured with field measurement instrumentation and closed-loop control, while its high-precision excitation power supplies can support a magnetic-field control mode when paired with an appropriate gaussmeter. Cryomagtech
17. Where Should the Probe Be Located in Closed-Loop Operation?
This deserves attention before ordering.
If the probe occupies the same physical location as the sample, a conflict appears:
The probe and the DUT cannot occupy the same space simultaneously.
Possible architectures include:
Reference Probe Near the Sample
The probe is permanently installed near the working region.
Advantages:
- Continuous feedback
- Simple automation
Limitation:
- Probe measures a nearby reference position rather than exactly the sample position
Removable Calibration Probe
The probe is inserted during calibration and removed during experiments.
Advantages:
- Can measure the actual sample location
Limitation:
- No direct real-time field feedback after removal
External Reference Sensor
A sensor is installed at another location and correlated to the sample field.
Advantages:
- Does not occupy sample space
Limitation:
- Requires a reliable relationship between reference and sample field
This mechanical question can change the complete system design.
18. A Mapping Kit Needs a Coordinate System
Once the probe moves, the system needs a spatial reference.
The mapping documentation should define:
- Origin
- +X direction
- +Y direction
- +Z direction
- Probe sensing axis
- Probe zero position
- Measurement grid
- Step size
Otherwise a spreadsheet containing:
| X | Y | Z | B |
|---|---|---|---|
| 0 | 0 | 0 | 0.500 |
| 10 | 0 | 0 | 0.498 |
| 20 | 0 | 0 | 0.492 |
is incomplete.
Ten millimeters in which direction?
From which origin?
With which probe orientation?
Good field mapping is as much a documentation problem as a measurement problem.
19. Manual or Motorized Mapping?
This depends on how often mapping will be performed.
Manual Mapping
Suitable when:
- Mapping is infrequent
- Number of points is small
- Budget is limited
- Required positioning tolerance is moderate
Typical components:
- Manual XYZ stage
- Position scale
- Probe fixture
- Gaussmeter
- Spreadsheet or basic software
Motorized Mapping
More suitable when:
- Hundreds or thousands of points are required
- Mapping must be repeated frequently
- 3D field volumes are being characterized
- Automated reports are required
- Operator-dependent positioning must be reduced
Typical additions:
- Motorized XYZ stages
- Motion controller
- Automated data acquisition
- Mapping software
- Coordinate synchronization
Do not specify motorization just because it sounds more sophisticated.
Specify it because the mapping workload justifies it.
20. What Should Be Included in the Delivery Documentation?
Hardware alone does not make a system complete.
A proper documentation package can be equally important.
Depending on project scope, buyers may request:
Equipment Documentation
- System configuration list
- Model and serial numbers
- Electrical requirements
- Cooling requirements
- Drawings
- Interface definitions
Magnet Performance Data
- Field-versus-current curve
- Pole gap used during testing
- Coil constant where applicable
- Maximum operating conditions
- Thermal or duty-cycle information
Measurement Documentation
- Probe identification
- Gaussmeter identification
- Calibration information
- Measurement conditions
- Probe orientation
Mapping Documentation
- Mapping coordinates
- Measurement grid
- Raw field data
- Uniformity calculation
- Graphical field map
- Test date
Acceptance Documentation
- Factory Acceptance Test results
- Pass/fail criteria
- Deviations
- Final configuration record
For future troubleshooting, this documentation may be more valuable than an impressive brochure.
21. Calibration Certificate, Factory Test Report, and Mapping Report Are Not the Same Thing
These documents are frequently confused.
Calibration Certificate
Typically relates to a measurement instrument or measurement result and should clearly identify the calibrated item, conditions, results, and applicable uncertainty or traceability information.
Factory Test Report
Demonstrates that the delivered system met defined production or acceptance tests.
For example:
- Maximum field achieved
- Current stability
- Protection functions
- Cooling operation
Field Mapping Report
Describes the spatial magnetic field distribution.
For example:
- Measurement coordinates
- Field values
- Uniformity
- Field contours
- Mapping conditions
One document does not automatically replace the others.
22. Why Measurement Uncertainty Matters in Acceptance
Suppose the tender states:
Uniformity ≤1.0%
and the supplier measures:
0.95%
Is that definitely a pass?
Not necessarily.
The result depends partly on the measurement uncertainty.
NIST’s guidance on calibration emphasizes that calibration compares an instrument or item with reference standards, while uncertainty describes how confidently calibrated results relate to the reference basis. NIST
This does not mean every research magnet tender needs a complicated uncertainty budget.
But when acceptance tolerances become tight, the measurement method must be sufficiently accurate to distinguish pass from fail.
A 1% specification should not be verified using a measurement process with uncontrolled errors of similar magnitude.
23. Five Common Scope Mistakes in Magnetic Field System Procurement
Mistake 1: Buying a Magnet and Assuming the Power Supply Is Included
Always list the excitation system explicitly.
Mistake 2: Buying a Power Supply and Assuming It Measures the Magnetic Field
Current measurement is not field measurement.
Mistake 3: Asking for Uniformity Without Defining a Measurement Volume
A percentage without a region cannot be meaningfully verified.
Mistake 4: Asking for “Calibration” Without Defining the Deliverable
Clarify whether you need:
- Instrument calibration
- Coil constant calibration
- Field verification
- Full spatial mapping
Mistake 5: Asking for Field Mapping Without Saying Who Needs the Mapping Equipment
Specify whether the supplier should:
- Perform mapping only, or
- Deliver the complete mapping kit
These five questions can eliminate a surprising amount of quotation confusion.
24. A Practical Four-Level Purchasing Model
Buyers can simplify procurement by thinking in four levels.
Level A — Magnet Only
Includes:
- Magnet or coil assembly
Best for:
- Experienced integrators
- Laboratories with existing infrastructure
Level B — Magnetic Field Generator
Includes:
- Magnet
- Power supply
- Required cooling/interface components
Best for:
- Laboratories that already own measurement instruments
Level C — Measured Magnetic Field System
Includes:
- Magnet
- Power supply
- Gaussmeter
- Probe
- Basic control
- Probe fixture
Best for:
- Research measurements
- Field-controlled experiments
- Repeatable verification
Level D — Complete Field Generation + Mapping System
Includes:
- Magnet
- Power supply
- Gaussmeter
- Probe
- Mapping stage or fixture
- Control software
- Mapping software
- Field characterization
- Acceptance documentation
Best for:
- Calibration laboratories
- Magnetometer testing
- IMU testing
- Field uniformity validation
- Sensor production
- System integration
- Tender projects with formal acceptance criteria
There is no universally “correct” level.
The correct package is the lowest level that still allows the user to complete the intended experiment without discovering critical missing infrastructure after delivery.
25. A Better RFQ Checklist for Buyers
Before requesting a quotation, answer these questions.
Magnetic Field Requirement
- Required field range?
- DC, AC, or both?
- One axis or multiple axes?
- Required working volume?
- Required uniformity?
Control Requirement
- Current control or field control?
- Manual or computer control?
- Open-loop or closed-loop?
- Required sweep functions?
Measurement Requirement
- Is a gaussmeter required?
- Is a probe required?
- Single-axis or three-axis probe?
- Required measurement range?
- Calibration documentation required?
Mapping Requirement
- Is one-point verification enough?
- 1D, 2D, or 3D mapping?
- Manual or motorized?
- Required grid spacing?
- Must mapping hardware be delivered?
Acceptance Requirement
- Which parameters will be tested?
- At what operating conditions?
- What is the pass/fail criterion?
- What documentation must be supplied?
Once these questions are answered, quotation comparison becomes much easier.
26. Advice for Tender Buyers: Specify Deliverables, Not Assumptions
A strong tender should explicitly list what must arrive at the customer’s site.
For example:
System delivery shall include:
- Electromagnet assembly
- Matched bipolar excitation power supply
- Water-cooling unit where required
- Gaussmeter
- Appropriate magnetic field probe
- Probe positioning fixture
- System control software
- Communication cables
- Field-versus-current characterization
- Uniformity mapping report over the defined working volume
- Operating documentation
Or, if the buyer already owns instrumentation:
Gaussmeter, probe, and field mapping hardware are excluded from supplier scope. Supplier shall provide factory field mapping data using calibrated measurement equipment.
Both specifications are clear.
The dangerous version is:
“Complete magnetic field system.”
without defining what “complete” means.
27. Advice for Distributors and System Integrators
Intermediaries should be particularly careful.
An end user may ask:
“We need a Helmholtz coil for magnetometer calibration.”
That does not yet tell you whether they expect:
- Coil only
- Coil + power supply
- Coil + three power supplies
- Coil + gaussmeter
- Coil + reference probe
- Closed-loop control
- Fixture
- Mapping system
- Sensor calibration software
Before sending the requirement to the manufacturer, translate the application into an explicit scope.
Otherwise the quotation may look cheaper initially but fail to include what the end user actually expects.
28. Where Cryomagtech Magnet & Field Systems Fit
Cryomagtech’s Magnet & Field Systems cover both individual magnetic field generation components and integrated system configurations.
Depending on the project, the architecture can include:
- Electromagnet
- Helmholtz coil
- High-precision bipolar power supply
- Gaussmeter
- Hall probe
- Field feedback
- PC control
- Sample or probe positioning
- Customized magnetic field integration
Cryomagtech’s current product architecture includes standalone electromagnets as well as integrated electromagnet and Helmholtz coil field-generation systems. Cryomagtech
For a quotation, the most useful starting point is not simply:
“Please quote a magnet.”
It is:
“This is the field we need, this is where we need it, this is how we intend to verify it, and this is what we expect to receive.”
That gives both buyer and supplier a much cleaner engineering boundary.
29. Key Takeaways
The boundary between a magnet and a complete magnetic field system should be defined before purchase.
Remember:
- A magnet generates field but may not include excitation electronics.
- A power supply controls electrical excitation, not necessarily the actual field.
- A gaussmeter and probe allow direct field measurement.
- A probe fixture determines whether measurements are repeatable.
- One field measurement does not demonstrate spatial uniformity.
- Field mapping requires a defined volume and coordinate system.
- Factory mapping does not automatically give the customer future mapping capability.
- Closed-loop field control makes the probe part of the control system.
- Calibration certificates, factory test reports, and mapping reports serve different purposes.
- Tight acceptance limits require an appropriate measurement method.
- “Complete system” should always be translated into an explicit delivery list.
The right question is therefore not:
“Should we buy the mapping kit?”
It is:
“What must we be able to prove, reproduce, or measure after the supplier leaves?”
Once that question is answered, the correct delivery scope usually becomes clear.
References
1. NIST — Policy on Metrological Traceability
NIST explains that metrological traceability requires a documented, unbroken chain of calibrations, with measurement uncertainty associated with each link. This is directly relevant when specifying calibrated probes, measurement instrumentation, and acceptance data in magnetic field systems. NIST
NIST — Policy on Metrological Traceability
2. NIST/SEMATECH — Issues in Calibration
The NIST/SEMATECH Engineering Statistics Handbook explains calibration as comparison with reference standards and discusses how calibration reduces measurement bias. This supports the distinction between simply generating a field and measuring or verifying it using suitable instrumentation. NIST