Pass/Fail Limits and Why the Test Point Matters

How the same device can pass at one value, fail at another, and why testing the right point matters

A medical device does not always perform the same way across its entire operating range.

Published August 16, 2026 · Revised September 5, 2026

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What This Page Explains

This page covers:

The Simple Version

A test point is the exact setting or operating condition being checked. The pass/fail limit is the acceptable result at that point. If an infusion pump set to 100 mL/hr must measure between 95 and 105 mL/hr, a result inside that window proves performance at 100 mL/hr under the stated test conditions. It does not prove that the pump performs correctly at 1 mL/hr or 999 mL/hr.

That is why service procedures often specify low, middle, and high points. Low-rate testing may expose resolution, friction, or intermittent delivery problems. High-rate testing may expose restrictions, weak drive systems, pressure effects, or gain errors. Substituting one convenient middle point removes the very coverage the manufacturer intended.

What Three Test Points Can Tell You

Imagine a pressure channel tested at 50, 150, and 250 mmHg. If every indication is about 5 mmHg high, the pattern suggests an offset. If the low point is close but the error grows as pressure rises, think about gain, span, compliance, or a range-dependent problem. If only the middle point fails, repeat the setup carefully and consider nonlinearity or an intermittent connection rather than forcing one adjustment to fit every point.

Record every required point, its applicable limit, and the actual unrounded result. Do not average a failed point together with passing points unless the manufacturer explicitly defines an averaging method. Each required point is normally its own pass/fail decision, and one failure means the tested function has not met the full procedure.

What Is a Test Point?

A test point is the specific value or condition where performance is checked.

Examples:

The manufacturer may require several test points for one function.

What Is a Pass/Fail Limit?

The pass/fail limit defines the acceptable result.

Example:

Reference:

100 mmHg.

Allowed accuracy:

±3 mmHg.

Pass range:

97 to 103 mmHg.

If the device reads:

102 mmHg

pass.

If it reads:

105 mmHg

fail.

Why Test at More Than One Point?

Because errors are not always constant.

A device may behave differently at:

Multiple points help reveal patterns.

Example: Pressure Channel

Reference → Device

50 → 50 100 → 100 200 → 220

The channel looks perfect at the first two points.

It fails badly at the high end.

A one-point test would have missed the failure.

Low-End Testing

Low values can be especially challenging.

Example:

Infusion pump set to:

1 mL/hr.

A small absolute error becomes a large percentage of the total flow.

That may reveal problems that are invisible at:

100 mL/hr.

Low-Flow Example

Pump set:

1.0 mL/hr.

Measured:

0.8 mL/hr.

Difference:

0.2 mL/hr.

That sounds tiny.

But it is:

20% low.

At a low test point, small absolute differences can matter a lot.

High-End Testing

High test points challenge different things.

Examples:

A device may perform normally in the middle and fail near maximum output.

Mid-Range Testing

Mid-range points often provide a useful general accuracy check.

But they should not automatically replace low and high points when the manufacturer requires them.

Multiple Points Reveal Error Patterns

Suppose a pressure channel gives:

Reference → Device

50 → 55 100 → 105 200 → 205

That is a consistent:

+5 mmHg

offset.

Now:

50 → 52 100 → 104 200 → 208

The error grows with the value.

That looks more like a gain or scaling issue.

The pattern across test points tells you more than one measurement.

Offset Error

An offset means the measurement is shifted by roughly the same amount.

Example:

Actual:

0.

Displayed:

+5.

Actual:

100.

Displayed:

105.

Actual:

200.

Displayed:

205.

The error stays near:

+5.

Gain Error

A gain error grows with the measurement.

Example:

Actual:

50.

Displayed:

55.

Actual:

100.

Displayed:

110.

Actual:

200.

Displayed:

220.

The device increasingly overreads as the input increases.

Nonlinear Error

Sometimes the error does not follow a simple pattern.

Example:

50 → 50 100 → 101 200 → 225

That may suggest:

Multiple points reveal it.

Why Manufacturer Test Points Matter

The manufacturer may choose points because they:

Do not assume you know better without a valid approved procedure.

Do Not Substitute Convenient Values

Suppose the procedure says:

Test at:

50, 100, and 200 mmHg.

You test:

100 mmHg only

because it is easy.

You have not completed the required test.

Do Not Replace a Test Point With “Close Enough”

Required:

200 J.

You test:

150 J.

That may prove the defibrillator works at 150 J.

It does not prove it passes at 200 J.

Different Test Points May Have Different Tolerances

A manufacturer may specify:

Low range:

±2 units.

High range:

±5%.

Do not apply the same limit everywhere.

Example

Pressure range:

0–50 mmHg:

±2 mmHg.

Above 50 mmHg:

±3%.

At:

25 mmHg

acceptable:

23 to 27.

At:

200 mmHg

acceptable:

194 to 206.

The tolerance changes with the test point.

Percentage Tolerance Changes the Absolute Limit

Suppose tolerance:

±5%.

At:

10 mL/hr

allowed error:

0.5 mL/hr.

At:

100 mL/hr

allowed error:

5 mL/hr.

At:

500 mL/hr

allowed error:

25 mL/hr.

Same percentage.

Different absolute limits.

Maximum Limits

Some tests only care about an upper boundary.

Example:

Leak rate:

Maximum 100 mL/min.

Test result:

80.

Pass.

Result:

120.

Fail.

The exact test condition still matters.

Minimum Limits

Example:

Battery runtime:

Minimum 90 minutes.

Battery runs:

95 minutes.

Pass.

Battery runs:

88 minutes.

Fail.

Again, that only applies under the defined runtime conditions.

Threshold Testing

Some functions are tested to determine when a device responds.

Examples:

The test point may be the point where behavior changes.

Alarm Example

High-pressure alarm set:

40 cmH2O.

Manufacturer allows activation within:

±2 cmH2O.

Alarm activates at:

41.

Pass.

Activates at:

46.

Fail.

You are testing the threshold, not just whether an alarm eventually occurs.

Why Test Points Matter for Alarms

If you simply increase pressure until the alarm sounds, you prove:

The alarm can activate.

You do not prove:

It activates at the correct threshold.

That distinction matters.

Occlusion Example

Infusion pump occlusion limit:

Specified range:

8 to 12 psi.

Measured activation:

9.5 psi.

Pass.

Measured:

15 psi.

Fail.

Again, the exact activation point matters.

Electrical Test Points

“Test point” can also mean a physical measurement location.

Example:

Measure:

24 VDC at TP4.

That location matters because voltage may change throughout the circuit.

Physical Test Point vs Performance Test Point

There are two related meanings.

Performance Test Point

A value you apply or command.

Example:

100 mmHg.

Electrical Test Point

A physical location where you measure.

Example:

TP3 on power board.

Both matter because the result is only meaningful at the correct point.

Voltage Drop Example

Power supply output:

24.0 VDC.

At main board:

21.5 VDC.

If the specification applies at power-supply output, the supply may pass.

The downstream wiring may be the problem.

Where you measure matters.

Load Condition Matters Too

A voltage specification may apply:

A supply may pass at idle and fail when load increases.

Example

24 V rail idle:

24.1 V.

Motor runs:

19.2 V.

If the specification requires:

22.8 to 25.2 V

under operating load, the device fails.

You had to test at the correct operating point.

Timing Can Be a Test Point

Some measurements must be made:

A value measured at the wrong time may be meaningless.

Example

Motor drive output:

0 V

while motor is stopped.

That may be normal.

You need to measure while the motor is commanded.

Test Point and Device Mode

Device mode can affect specifications.

Examples:

Make sure you test in the mode required by the procedure.

Patient Simulators

A patient simulator may provide specific test values.

Example:

Heart rate:

60 bpm 120 bpm 180 bpm

Those are test points.

The monitor should respond appropriately at each one if required by the procedure.

Why Multiple Heart-Rate Points Matter

A monitor may read:

60 correctly

and:

180 incorrectly.

A single normal-rate test would miss the failure.

Defibrillator Energy Testing

A procedure may require:

because energy delivery can behave differently across the range.

Do not assume one successful shock proves all settings.

Infusion Pump Testing

A pump may need testing at:

because different mechanical or control behaviors may dominate.

Ventilator Testing

A ventilator may require checks at multiple:

because performance can vary across the operating range.

Pressure Sensor Testing

A pressure sensor may pass at zero and fail at high pressure.

That is why multi-point calibration and verification exist.

Temperature Testing

Temperature systems may need multiple test temperatures.

Example:

32°C 37°C 42°C

This can reveal:

A single 37°C check only proves one point.

Zero Is Also a Test Point

Zero can be extremely important.

Example:

Pressure input:

0 mmHg.

Device reads:

8 mmHg.

That offset will affect the entire range.

Do not ignore the zero condition when the procedure includes it.

Zeroing Before Testing

Some devices require a zero or baseline procedure before measurement.

If you skip that step, all later test points may be wrong.

Calibration Points vs Verification Points

Calibration points are used to adjust the system.

Verification points confirm performance.

They may not always be the same.

Follow the manufacturer sequence.

Do Not Calibrate Only the Failing Point Without Understanding the Procedure

Changing one calibration point may affect:

Complete the full approved procedure.

Recheck All Required Points After Adjustment

If you calibrate at:

100 mmHg

do not stop because that point now passes.

Retest all required verification points.

Borderline Test Points

Suppose pass limit:

95 to 105.

Measured:

105.0.

That may be within limit.

But repeated measurements:

104.9 105.2 105.1

show unstable performance around the boundary.

Follow the manufacturer's required method.

Repeatability Matters

If repeated measurements vary widely, even if some pass, the device may have another problem.

Example:

100 93 106 99

That poor repeatability is useful evidence.

Do Not Choose the Best Result

If the first test fails and the fifth test passes, do not simply record the passing one.

Follow the defined test method.

Test Setup Is Part of the Test Point

The same commanded value can produce different results if:

The complete setup matters.

Example: Ventilator

Set:

500 mL.

Different test lung compliance:

Different measured behavior.

If the manufacturer defines a specific test setup, use it.

Example: NIBP

Reference:

200 mmHg.

Leaking hose:

Device appears inaccurate.

Known-good hose:

Passes.

The failed test was caused by setup, not the monitor.

Environmental Conditions

A test point may only be valid within defined:

conditions.

Do not ignore the environment.

Test Equipment Range

Your analyzer must also be appropriate for the test point.

If you are testing:

300 mmHg

but the analyzer is rated only to:

200 mmHg,

you cannot use it for that point.

Test Equipment Accuracy Can Change Across Its Range

An analyzer may have different performance at different points.

Read its specification too.

Example

Pressure analyzer accuracy:

Excellent from:

0–200 mmHg.

Reduced above:

200 mmHg.

That may affect whether it is suitable for a high-range device test.

Why High and Low Points Are Often More Revealing

Middle-range operation is often the easiest operating condition.

Extremes can expose:

That is why manufacturers often choose them.

Do Not Create a Pass/Fail Limit From Experience

Avoid:

These usually read around 95, so that's fine.

Use the defined requirement.

Experience can guide troubleshooting.

Specifications determine objective acceptance.

Do Not Move the Goalposts After Seeing the Result

If you calculated:

Pass:

95 to 105.

Then measure:

106.

Do not decide:

106 is basically 105.

The limit was known before the test.

Apply it consistently.

Real-World Example: Infusion Pump

Required points:

1 mL/hr 100 mL/hr 500 mL/hr

Results:

1 → 0.7 100 → 99 500 → 498

Two points look excellent.

Low flow fails.

Without the low-flow point, the problem would be missed.

Real-World Example: Pressure Channel

Test:

0 mmHg → displays 8

100 → 108

200 → 208

Consistent offset.

Zero point exposes the pattern immediately.

Real-World Example: Defibrillator

Low energy:

Pass.

Mid energy:

Pass.

High energy:

Fails low.

Possible areas include:

The high test point reveals a load-dependent failure.

Real-World Example: Ventilator

500 mL:

Pass.

100 mL:

Fail.

Low-volume delivery may reveal:

One normal adult test point would not prove performance in the lower range.

Real-World Example: Power Supply

Idle:

24.2 V.

Under compressor load:

20.9 V.

The supply passes at one operating point and fails at another.

The load condition is the important test point.

Common Mistakes

Testing Only One Convenient Point

Use all required points.

Assuming Mid-Range Performance Represents the Whole Range

It may not.

Applying the Same Tolerance Everywhere

Check range-specific limits.

Measuring at the Wrong Physical Location

Use the specified point.

Ignoring Operating Mode

Conditions matter.

Choosing the Best Repeated Result

Follow the required test method.

Testing the Right Value With the Wrong Setup

The whole test condition matters.

Moving the Pass/Fail Limit Because the Result Is Close

Apply limits consistently.

A Useful Test-Point Framework

For each test, identify:

Test Point

What value or condition am I applying?

Expected Result

What should the device do?

Acceptance Limit

What range passes?

Actual Result

What did I measure?

Decision

Pass or fail?

Then move to the next required point.

Another Useful Question

Ask:

What part of the device's operating range have I actually challenged?

If you only tested the middle, you may know very little about the edges.

What Did You Actually Prove?

Suppose a pump delivers:

100 mL/hr

within tolerance.

You proved:

The pump met the specified requirement at 100 mL/hr under the conditions tested.

You did not prove:

Each test point supports a specific conclusion.

Final Thoughts for Biomeds

A passing measurement only means something in context.

You need to know:

That is why test points matter.

A device can look perfect in the middle of its range and fail badly at the edges.

A power supply can look perfect at idle and collapse under load.

An alarm can activate but still activate at the wrong threshold.

So do not ask only:

Did it pass?

Ask:

What did it pass?

At what point?

Under what condition?

When you understand that, your testing becomes much more meaningful.

— Jake

Important Note

Required test points, acceptance limits, operating conditions, measurement locations, and post-calibration verification procedures vary by manufacturer, model, hardware revision, and software version. Follow current manufacturer documentation, approved facility procedures, and appropriately maintained test equipment when making pass/fail or return-to-service decisions.

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