What Is an Indicator Gauge?
An Indicator Gauge refers to an instrument that converts physical quantities such as temperature, pressure, flow, and weight into a readable form and displays them for human interpretation.
In various locations, including factories, machinery, and equipment in motion, monitoring various physical quantities such as temperature, humidity, flow, weight, and rotational speed is essential. Measurements of physical quantities are performed by sensors specific to each purpose, and the measured values are transmitted in electrical form.
There are analog indicator gauges and digital indicator gauges. They receive electrical signals from sensors and convert the values into a format understandable by humans for display. Additionally, some instruments, known as indicator controllers, not only display values but also have adjustment functions to bring parameters like temperature and humidity closer to target values. Sometimes, the term “indicator gauge” may also include indicator controllers.
Uses of Indicator Gauge
Indicator gauges are widely used in various locations, including factories and facilities, to monitor physical quantities of machinery in operation. Especially in facilities such as power plants, substations, and plants, numerous indicator gauges are embedded in control panels to monitor equipment conditions intensively. They are also utilized on ships to monitor the status of engines, boilers, etc., and even the electricity meters installed in residential houses are a type of indicator gauge.
The displayed physical quantities vary widely. In factories, they are used to display and monitor the temperature, pressure, and flow of gases and liquids, as well as the power and speed of machinery. Additionally, they are employed for the display and monitoring of various physical quantities such as humidity, illumination, sound volume, weight, and distance.
Indicator gauges also serve the role of notifying when monitored physical quantities reach a warning level. Analog types typically use a red-colored portion of the scale to indicate the warning range when the needle touches it. Digital types, on the other hand, present a warning level, and when the measured value reaches that level, they alert through alarms or lights. An indicator gauge with an alarm function is also referred to as an indicator alarm gauge.
Principles of Indicator Gauge
Indicator gauges include analog and digital types, each with different principles.
1. Analog Indicator Gauge
Analog indicator gauges, also known as analog electric meters, quantitatively indicate the input electrical quantity using the amplitude of needle deflection. They do not require an external power source and consist of driving, controlling, and braking mechanisms.
The driving mechanism generates a driving torque corresponding to the input electrical quantity, causing the needle on the meter to move. The controlling mechanism generates a controlling torque in the opposite direction to the driving torque using mechanisms like springs. The point where the driving torque and controlling torque balance is where the needle indicates the value. The braking mechanism suppresses needle oscillation, ensuring the needle stops promptly at the equilibrium point.
Analog indicator gauges are classified into various types based on the principles of their driving mechanisms, such as movable coil type, rectifier type, current force type, induction type, electrostatic type, thermoelectric type, and movable iron piece type.
The most commonly used indicator gauge is the movable coil type. In this type, a movable coil is placed within the magnetic field created by a permanent magnet, similar to the principle of a motor. When current flows through the movable coil, its interaction with the magnetic field causes the coil to tilt. The tilt of the coil is balanced by the force of the spring (braking mechanism), and the point where it stops indicates the value of the current. Movable coil-type meters excel in frequency characteristics and are commonly used in DC voltage and current measurements.
2. Digital Indicator Gauge
Digital indicator gauges convert the measured value into an electrical current, digitally convert it using an A-D converter, and then count the generated pulses to display the result as a numerical value.
Most products come with various additional features, such as alarm functions. For instance, they may store measured values in internal memory over a certain period, displaying changes in values over time in a graph.
Moreover, digital indicator gauges can perform multiple measurements with one device, process data at intervals, and display individual measurement results. Since the output is a digital signal, it can be sent to a network. By collecting results from multiple digital indicator gauges into one computer, monitoring the entire facility becomes possible. In many cases, software for the PC side is provided to establish a PC and network for digital indicator gauges.
How to Choose Indicator Gauge
The current mainstream of indicator gauges is digital. Various digital indicator gauges with multiple additional features are commercially available. When choosing a digital indicator gauge, it is advisable to verify that the basic specifications and environmental resistance meet the requirements and then select a product with convenient features tailored to the usage scenario.
On the other hand, analog indicator gauges have advantages such as not requiring a power source, excellent durability, and reliability, and are suitable for intuitive readings. The way the needle deflects allows for analog diagnostics, such as assessing the condition of machinery based on needle movement.