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1.What is Density & Specific Gravity of liquid? Why is it important for operation of float level switches and transmitters?

Density - It is defined as ratio of mass divided by volume of liquid/substance.

Specific Gravity – It is a ratio of density of liquid/substance to density of water.In metric system, value of density of water is one. Hence in metric system, numerical value of density and specific gravity are same.

In order tostay on the surface of liquid, the float used in float switches & transmitters, must have specific gravity less than that of the liquid for which it is used.

2.What is meant by NO contact or NC contact?

‘NO’ means Normally Open contact when switch is not actuated.

‘NC’ means Normally Close contact when switch is not actuated

3.What is SPDT & DPDT contact?

SPDT - Single Pole Double Throw i.e. NO P NC contact

DPDT – Double Pole Double Throw, i.e.  2NO,  2P,  2NC contacts

4.What is potential free contact or dry contact?

Potential free contacts are also called dry contacts or voltage-free contacts as it is not providedwith any voltage.

5.What is level gauge, level switch & level transmitter?

Level Gauge - is a completely mechanical instrument through which one can visually see the actual level in the tank. It is based on the principle of communicating levels of liquids in the vessel and the gauge or external chamber. Level gauges are also based on Archimedes principle of floating body & magnetism. 

Level Switch–In many cases seeing the liquid level through the gauge is not sufficient. To control motor/pump automatically, we require switching signal i.e. make (NC) and break (NO) contacts when level reaches to particular set point. Techtrolmanufactures variety of single point or multi pointlevel switches.  In most of level switches, either reed switches or micro switches or relays are used to providepotential free NO or NC contacts. Some level switches provide PNP/NPN switching output. When particular level set point is reached the corresponding switch operates and contacts change over from NO to NC or vice versa. Output of switch is potential free open or close contact

Level Transmitter – It gives continuous analog/digital output against zero to 100% of liquid level in the tank.  Analog output is 4-20mA or 1 to 5VDC and digital output is in the form of RS485 Modbus or HART. The output of the transmitter can be transmitted to a remote place and can be connected to Techtrol Indicator Controllers (TLIC/TLICP/TUIC) or PLC /SCADA to monitor and control the liquid level.

6.Why there are different types of level gauges, switches and transmitters?

Pune Techtrol manufactures various types of level gauges, switches & transmitters based on different principles. They are selected according to

  1. Application desired.
  2. Operating conditions (pressure & temperature)
  3. Type of liquid/solid, its inherent characteristics such as specific gravity, conductivity, viscosity, vapor/foam formation.
  4. Compatibility of liquid to wetted parts.
  5. Mounting position on the tank.

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