Pressure Gauge vs Pressure Transmitter vs Manometer: What Is the Difference?

A pressure gauge shows pressure locally on a dial or display, a pressure transmitter converts pressure into a standard electrical signal such as 4 to 20 mA for a control system, and a manometer measures pressure (most often small pressure differences) using a column of liquid or, in modern form, a digital sensor. The right choice depends on who or what needs the reading. Use a gauge when a person reads it on the spot, a transmitter when a PLC or logger needs the data, and a manometer for low pressure, draft or differential measurements. This guide compares the three side by side and explains related terms such as transducer, sensor, switch and indicator.

Quick comparison

What is a pressure gauge?

A pressure gauge is an indicator. It shows the pressure at a point in a system for the person standing in front of it. Mechanical gauges use a Bourdon tube or a capsule to move a pointer, and need no power. Digital gauges use an electronic sensor and a display, as explained in our digital pressure gauge buying guide. For the mechanical principle, see Bourdon tube pressure gauges explained.

Gauges are the best choice when:

• An operator needs a quick visual check at the machine.
• No power is available at the measurement point.
• You want a low-cost, robust and simple solution.
• A technician is testing or commissioning and wants an instant reading.

What is a pressure transmitter?

A pressure transmitter contains a sensing element, usually a strain gauge or a piezoresistive element on a diaphragm, plus electronics that amplify and condition the signal. The output is a standard signal that a PLC, a controller or a data logger can read. The most common is a 4 to 20 mA current loop, where 4 mA represents the bottom of the range and 20 mA represents the top. Voltage outputs such as 0 to 10 V are also common.

The 4 to 20 mA signal is popular for good reasons:

• It tolerates long cable runs and electrical noise better than a low-level voltage signal.
• A reading of 0 mA tells you the loop is broken, because a live signal never drops below 4 mA.
• Many devices can be wired in series on the same loop.

Transmitters suit applications that need automatic control, trending, alarms or remote monitoring. A pump station, for example, might use a transmitter to start and stop pumps at set pressures and to log the data.

An example from our range

The WIKA Model A-10 pressure sensor, which we supply, is a compact pressure sensor for general industrial applications. It has a 316L stainless steel case and wetted parts, is available for gauge, absolute and compound pressure, and offers 4 to 20 mA and 0 to 10 V output signals. See the Pressure Sensor SNG-A10 page, and our WIKA pressure gauge guide for background.

What is a manometer?

A traditional manometer is a U-shaped tube partly filled with liquid, such as water, oil or mercury. One side connects to the pressure being measured, and the other is open to air or to a second pressure. The difference in liquid height shows the pressure difference. Inclined-tube manometers magnify small pressure differences, which is why they have been used for draft and low air pressure.

Modern digital manometers use an electronic differential sensor instead of liquid. They are widely used to check filter pressure drops, ventilation, cleanroom pressure and gas appliance pressure. In search results you will see the same instrument called a digital manometer or a differential pressure gauge. The calibration of these devices is covered in our article on the calibration of manometers.

Pressure gauge vs pressure transducer

The words transducer and transmitter are often used loosely, but they usually mean different things:

• Transducer: converts pressure into a low-level electrical signal, such as millivolts per volt, that needs an external amplifier or data acquisition system.
• Transmitter: includes the amplification, so the output is a standard signal such as 4 to 20 mA or 0 to 10 V that is ready for a controller.
• Sensor: a general term for either, depending on the manufacturer. Check the datasheet to see the actual output.

The key point is to check the output signal on the datasheet before you buy, and make sure your controller can read it.

Pressure gauge vs pressure switch

A pressure switch does not measure the pressure continuously. It changes an electrical contact when pressure crosses a set point, which makes it a simple on/off control for pumps and compressors, or a safety alarm. A switch tells you that a limit has been reached, while a gauge or transmitter tells you how far from the limit you are. Many installations use a gauge, a switch and a transmitter together.

Pressure gauge vs pressure indicator

An indicator is another word for a gauge that displays a value. In some industries, a digital pressure indicator means a handheld or panel unit that shows the reading from a separate sensor. The terms overlap, so look at what the device actually does: does it show a reading, send a signal, or both?

Gauge vs absolute pressure

Another common search is about the difference between gauge and absolute pressure. Gauge pressure is measured relative to the atmosphere, so an open tank reads zero. Absolute pressure is measured relative to a perfect vacuum, so the same tank reads about 101.3 kPa at sea level. Absolute sensors are used where atmospheric changes would affect the result, such as vacuum processes and altitude measurement. The A-10 sensor is offered for gauge, absolute and compound types.

Differential pressure

A differential pressure device compares two pressures and reports the difference. It has two ports instead of one. Typical uses include filter monitoring, flow measurement across an orifice plate and level measurement in closed tanks. Differential instruments come as mechanical gauges, digital manometers and transmitters, so the same selection logic applies: choose the output that suits the person or system that needs the reading.

How to choose: a simple decision guide

1. Who reads it? If a person reads it at the point of measurement, choose a gauge.
2. Does a system need the data? If a PLC, SCADA system or logger needs it, choose a transmitter.
3. Is it a small pressure difference? If you are checking draft, filters or ventilation, choose a manometer or differential gauge.
4. Do you need an alarm or a trip? Add a pressure switch, or use the transmitter with alarm logic in the controller.
5. Do you need both local and remote readings? Fit a gauge and a transmitter on the same line, often through a manifold.
6. How accurate must it be? Compare the accuracy figures. Our range includes digital gauges from 0.5% down to 0.025% of full scale, as covered in the digital pressure gauge buying guide.
7. What are the conditions? Check temperature, vibration, media and ingress protection.

Installation tips that apply to all three

• Use an isolation valve so you can remove the instrument without shutting down the line.
• Choose the range carefully. Our pressure gauge range selection guide explains the method.
• Match the thread and mounting. See pressure gauge connection types and thread sizes.
• Protect against pulsation with a snubber or restrictor.
• Keep impulse lines short, and slope them to avoid trapped air or liquid.
• Calibrate at regular intervals. See pressure gauge calibration.

Putting it together on a real system

On a typical pump skid, you might fit a liquid filled gauge on the discharge for the operator, a transmitter that sends the same pressure to the PLC for control and alarms, and a pressure switch as an independent safety trip. A portable digital manometer or gauge then serves for commissioning and fault finding. Each device has a different job, and using the right one in each place gives you visibility, automation and safety without paying for more than you need.

Frequently asked questions

Can a pressure gauge replace a transmitter?

Only if no system needs the data. A gauge cannot send a signal to a controller.

Can a transmitter replace a gauge?

Not where an operator needs a local reading with no power. Many sites keep a gauge next to each transmitter as a backup and a sanity check.

What does 4 to 20 mA mean?

It is a current signal that represents the measured range. For a 0 to 10 bar transmitter, 4 mA is 0 bar and 20 mA is 10 bar, so 12 mA is 5 bar.

Is a digital pressure gauge a transmitter?

Not unless it has an output. A digital gauge shows a reading locally. Some, like the PDR1000, offer an optional analogue output for connection to compatible systems.

Which is more accurate, a gauge or a transmitter?

It depends on the model. Compare the accuracy specifications, the stability over time and the conditions of use rather than the device type.

Talk to us

If you are unsure whether you need a gauge, a sensor or both, send us your application details. You can also browse the pressure gauges, digital pressure gauges and pressure sensor categories.