Common sense in selecting pressure sensors

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  • Time of issue:2020-07-10 13:31
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Common sense in selecting pressure sensors


1. Q: What kind of pressure does the sensor measure? The first thing you should consider is the maximum stress on your system.

A: Generally, the maximum pressure range of the pressure sensor you need should be 1.5 times the maximum pressure of your system. These additional pressure ranges we suggest are due to many systems, especially hydraulic and process control, having pressure spikes or continuous pulses. These spikes can reach five or even ten times the "maximum" pressure and can cause damage to sensors. Continuous high voltage pulse, close to or exceeding the maximum rated pressure of the sensor, will also shorten the life of the sensor. But simply increasing the sensor's pressure rating is not a foolproof solution, because it would sacrifice the sensor's resolution. You can use buffers to dampen spikes, but this is only a compromise because it slows down the sensor response time.

All pressure sensors are designed to withstand maximum pressure over 200 million cycles without compromising performance. When selecting sensors, you need to find a compromise between system performance and sensor lifetime.  

2. Q: What is the pressure medium?

A: Another key factor to consider when choosing a sensor is the medium being measured. Is there a viscous liquid or slurry in the pressure head? Is the sensor in contact with a dissolved or corrosive medium or with clean, dry air?  

3. Q: What precision does the sensor need to achieve?

A: Precision is a term manufacturers use to describe sensor output errors. These errors may be due to nonlinearity, hysteresis, unrepeatability, temperature, zero balance, correction, and humidity effects. Many manufacturers specify a combination of nonlinearity, hysteresis, and unrepeatability in accuracy. For many sensors, "accuracy" can be lower than the nominal value due to factors such as temperature, zero point equilibrium, etc.

The "Technical Terms" section explains these terms in more detail. It costs more to have a more accurate sensor, so does your system really need that accuracy? A system that USES high precision sensors and low resolution instruments is actually an inefficient solution.

4. Q: How is the temperature resistance of the sensor?

A: Pressure sensors, like all physical equipment systems, can be faulty or even unusable in extreme temperatures. Generally, each sensor will have two temperature ranges, namely the operating range and the compensation range. The scope of compensation is included in the scope of work.

Working range refers to the range within which the sensor can be exposed to the medium after electrification without damage. However, this does not mean that the performance will reach the nominal specification (temperature coefficient) when it is outside the compensation range.

The scope of compensation is generally a narrower range within the scope of work. Within this range, the sensor ensures that the nominal specification can be met. The change of temperature affects the sensor in two ways, one is to cause zero drift, the other is to affect the output of the whole range. The sensor specification shall list these errors as: ± X % full range /°C, ± X % reading /°C, ± X % full range throughout the temperature compensation range, or ± X % reading throughout the temperature compensation range. Not having these parameters can cause uncertainty in your usage. Is the change in sensor output due to a change in pressure or a change in temperature? The temperature effect will be the most complex part of understanding how sensors are used.

5. Q: What output should be used?

A: Almost all sensors have millivolt output, or voltage amplification, or milliampere, or frequency output. The type of output you choose depends on the distance between your sensor and the system control or display, noise, and other electrical disturbances, as well as whether amplification is needed, the best position to place the amplifier, and so on. For many Oems, the distance between the control element and the sensor is short, so millivolt output is generally sufficient and low cost.

If you need to amplify the sensor output, it is easier to use another sensor with a built-in amplifier. Milliampere output or frequency output is required for long distance cables or areas with large electrical noise. In environments with strong RF and EMI, you may want to consider adding some additional shielding or filtering equipment to the MA and frequency output.

6. Q: What is the excitation voltage?  

A: The type of output may determine the excitation voltage you need. Many amplifying sensors have built-in voltage regulators that allow them to operate over a wide range of unadjusted voltage sources. Some sensors are proportional and require a modulated source of excitation. The power you use will determine whether you use the regulated power or not. This requires a compromise between the costs of the system and all the incentives.

7. Q: Do I need the sensor to be interchangeable?  

A: Is the interchangeability of sensors important for different systems, or do you correct every part of the system? This is a very important issue, especially for Oems. When you get your product to the customer, the cost of correcting it is very high. If your sensor is interchangeable, you can replace the sensor in the system and still keep the parameters the same.

8. Q: What degree of time stability is required for the sensor?  

A: Most sensors will "drift" over time. It is important to understand the sensor stability over a long period of time. This upfront work needs to reduce future problems.

9. Q: How strong does the sensor need to be?

A: One of the biggest headaches for users is what kind of mechanical strength the sensor needs, especially its casing. It is important to consider the environment in which the sensor will be applied. Is it in high humidity or water vapor? Is there a high intensity shock or impact? These issues should be considered when choosing a shell type.

Q: How do I connect the sensors to my own electrical system?  

A: Is the short cable on the sensor enough? Or, in long cable applications, is there a need for a connector to the sensor? Most pressure sensors can provide cables or connectors.

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