Panel Meter (Types, Input, Output, Sizes and Applications)

Analog Panel Meter

Analog panel meters receive the measured value from the input signal and display it directly without any intermediate change. 

In these devices, the interface is application-specific and can display any measurement unit with almost any input signal represented by the process. 

An analog panel meter can display speed, frequency, voltage, current, temperature, strokes per minute, or feet per second.

The actual input signals are AC or DC analog voltage or current. 0 to 10 volts DC, 4 to 20 milliamps DC or 0 to 100 volts DC are some examples of input signals. 

Some models can receive more than one input, such as pulsating frequencies known as multiple channel analog panel meters. 

There are two basic operation methods for displaying readings in analog panel meters. The first method is a taut band. 

There is a moving pointer or needle that hangs between two metal ribbons which reduces friction and improves sensitivity. These devices are resistant to high shocks making them suitable for use in rugged environments prone to high shocks.

Another method is a pivot and jewel in which the pointer is more stable for higher vibration environments but they are not as accurate as taut band panel meters. 

The operation method includes a coil & pointer being suspended by steel and is mounted in two jewel bearings.

Pivot & Jewel are commonly used for measuring alternating current while Taut band type is used for direct current measurement.

Digital Panel Meter

The digital panel meters provide the greatest resolution than analog panel meters and have an easier-to-read display, particularly in low light. 

The readings are the same in an analog and digital meter, but in cases where the input is constantly changing, it is better to use the analog panel meters.

For example, when using a motor the panel meter displays the number of amps that the motor draws at any given time through a shunt or CT. 

To ensure that the motor is drawing near 20 volts, an analog meter can be a good visual indication of the amps number that is being drawn. In this case, as the torque increases or decreases, the needle will fluctuate constantly within the range on the display. 

But if the panel meter is digital, it will be difficult for it to read constant changing numbers. Of course, this is not true for all applications. Using a digital meter is much easier to see numbers at a glance than an analog panel meter.

The digital meter can be adjusted to display several different parameters such as volts, amps, temperature, or any other engineering unit. 

The relay outputs are sometimes available and allow the panel meter to control a process depending on the measured input signal or display value.

Input Signal

For the correct operation, the device must be designed to receive analog input sent to it. The types of inputs are:

• AC Voltage - the input signal is accepted as a measurable form of AC voltage in volts AC (VAC).

• AC Current - the input signal is accepted as a measurable form of AC current in milliamps (mA AC) or amps (A AC).

• AC Power - the input signal is accepted as an adjustable range of AC current, voltage, and/or frequency.

• DC Voltage - the input signal is accepted as a measurable form of DC voltage in volts DC (VDC).

• DC Current - the input signal is accepted as a measurable form of DC current in milliamps (mA DC) or amps (A DC).

• DC Power - the input signal is accepted as an adjustable range of DC current, voltage, and/or frequency.

• Resistance - the input signal is accepted from elements that measure resistance change, like piezoresistive sensors or strain gauges.

• Temperature - the input signal is accepted from a thermocouple, RTD, or thermistor depending on a change in temperature.

Panel Meter Output

Basic Display Output

The main function that all digital panels are doing is receiving the input signal and converting it into a displayed value. 

This input is first transmitted from a sensor in the process, or system and is then sent to the device through the panel which the meter is connected to. The task of the panel is to provide the power for the device and inputs for the display.

Additional Outputs

In addition to the simple display, some digital panel meters provide optional control or interface functions.

Analog functionality: in this type, the device can provide an analog output (such as variable voltage or current) proportional to the input signal for use in analog devices.

Data interface: In this functionality the user can interact with the information that is displayed for data analysis.

Setpoint functionality: The user is allowed to determine input values that activate alarms or simple control functions.

Features

The digital panel meters may include several features that provide more functionality for the device including 

• Set point options
• Alarms
• On/off control
• Adjustable display

The features of panel meters are similar to the temperature controllers, so for more information about their features please refer to the temperature controller article.

Display

There are two types of panel meter display: numeric or alpha-numeric.

• Numeric: This type of panel meter displays only numbers. Most products have this kind of structure because the values that have to be displayed are mostly numbers. Also, most digital panel meters are numeric, because the main goal of meters is to represent numerical values.

• Alpha-numeric: In this type, both numbers and letters are displayed on the screen. This is suitable for complex signals as well as providing more information to the user, such as a reading's related channel or units.

Technology

The display of a panel meter can be either LED or LCD.

• LED (light-emitting diode) displays consist of diodes that light up the N-segment algorithm. The benefit of LED displays is that they can be seen in the dark.

• LCD (liquid crystal display) technology displays dark/black digits over a blank gray or green screen. LCDs consume less power compared to LEDs but need backlighting to be seen in the dark.

Number of Digits

The number of digits indicates how many digits there are in the display output. Depending on the desired accuracy, this number should be less than or equal to the number of significant figures in the signal input. 

In meters for displaying half digits like 4.5 digits or 2.5 digits, the first or the last digit can just be '1' or off, or '5' or off.

This "half" digit makes extending the upper limits of the display (1000 vs. _999) possible or provides the display of intermediate values (100.5 vs. 100_).

Panel Meter Size

Since meter panels are normally installed in the instrument panel, the panel must be cut to the size of the meter panels.

To provide switching conditions between panel meters, many panel meters are produced in standard DIN sizes.

Examples of Panel Meter

Totalizers: These panel meters receive the sum of an input signal in a certain period of time. Totalizers are generally useful to count pulse inputs or can be used in flow measurement applications.

Temperature and process panel meters: The most common type of panel meter is temperature and process panel meters. 

This type accepts a single channel input, displaying it digitally on the screen. Common inputs are received from temperature sensors such as RTDs and thermocouples.

Multi-input indicators: This is a type of digital meter that can take more than one input. Most meters have a switching button that displays the output of the next channel, while other types can scan all channels automatically and change their output periodically.

Panel Meter Applications

The panel meters are often installed inside the device panels. In addition to temperature measurement, they can also measure speed, pressure, current, and several other variables. 

For example, an air conditioner allows you to see the measured temperature on the instrument panel; this information is displayed with a panel meter.

Since digital panel meters are far more accurate and easier to read, digital panels are replaced by analog panels. We need a digital panel meter when what you’re measuring needs a high level of accuracy. 

Unlike their analog counterparts, the digital panel meters will be able to measure at different scales simultaneously. 

Also, since the digital panel offers you digital reading, you can maximize accuracy by changing the output to a smaller or larger measurement unit. 

There are different applications for panel meters and they have wide use in industrial, office, and laboratory settings. Here are some of their most common and useful applications:

Automobile

Panel meters are important instruments used in automobiles to display vital statistics related to a vehicle’s performance. 

The measured fuel, speed, and revolutions per minute (rpm) travel through their panel meter and are then displayed in an analog or digital format on an instrument panel (i.e., dashboard).

Airplane

Altitude, speed, and other related information in airplanes can be displayed through a panel meter. There are an overwhelming number of panel meters inside the cockpit of an airplane.

House

Panel meters are used all over the place in modern houses. For instance, the microwave oven’s instrument panel includes panel meters for measuring time, power, and weight. 

Radios and televisions use tuner devices to reproduce audio and video signals by using frequency and amplitude panel meters to interpret radio wave signals. A pressure gauge panel meter and motor rpm panel meter are used in water pumps to regulate water flow in a tank or swimming pool.

Motor current running 

In industries, fans or pumps running by a motor need to be monitored. In situations where there are deviations from the typical measurements panel meters are used to check the fan or pump for blockages or issues.

Oven temperature monitoring 

Industrial ovens are used for different applications such as curing rubber items. The digital panel meters connected to the temperature sensor can be used to precisely measure the temperatures. the measured temperature will be displayed on the screen of an instrument panel.

Pressure monitoring Since in some industries pressure monitoring is necessary, a pressure sensor can be used to send a current signal to a digital panel meter. by connecting the meter to an alarm. After reaching determined dangerous levels the alarm will be triggered and any unusual fluctuations easily identified.

You may be interested in reading the following articles in our website:

Tachometer (Working Principle, Types, Applications)

Temperature Controller And Process Controller