Showing posts from July, 2019

What is Class I Division 2?

A Class I Division 2 is a location: (1) In which volatile flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operation of equipment, or (2) In which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operation of the ventilating equipment. Class I Division 2 Classification Class I Division 2 refers to the ANSI/ISA 12.12.01 standard. This standard was previously UL1604 until UL recommended the newer ANSI/ISA standard be used and that all hazardous location products be certified under this standa

Steps to Selecting a Relay

Follow the steps below to select the correct electromechanical (EMRs) or solid state relay (SSRs) for your applications. 1.    Step 1. Identify mounting type: a.    Panel b.    DIN Rail c.    Plug-in d.    PCB 2.    Step 2. Identify Required Load Voltage Rating & Type: a.    AC or DC b.    Determine maximum voltage to be switched 3.    Step 3. Identify Required Load Current Rating: a.    Calculate Average Load current b.    Calculate Surge (inrush) current 4.    Step 4. Identify required circuit/switching arrangement: a.    Number of poles/circuits to be switched b.    Normally Open, Normally Closed or c.    Changover switching function 5.    Step 5. Identify Required Control Voltage & Type: a.    AC or DC b.    Control Voltage Range 6.    Step 6. Identify Load Type: a.    Inductive (Random Turn-on SSR) b.    Resistive (Zero Crossing SSR) 7.    Step 7. Identify Type of SSR Required: a.    Standard b.    Special Application: i.    Phase Angle Control ii.    Bur

Electromechanical Relays (EMRs) vs. Solid State Relays Comparison (SSRs)

Electromechanical Relays (EMR) Pros (Advantages) •    Lower initial cost compared to solid state relays. •    Provides complete electrical isolation. •    Tolerates high current & voltage transients. •    Insensitive to electromagnetic interference (EMI) / radio frequency interference (RFI). •    Higher open resistance (air gap). •    Lower closed resistance. •    Available with many poles/circuits (up to 8 or more). •    Many different circuit configurations available. •    Multiple packaging & feature options. •    Most typical failure mode is open.   Electromechanical Relays (EMR) Cons (Disadvantages) •    Higher control (coil) power consumption. •    Contact arcing can cause pitting & eventual open/short failure. •    Contacts can be affected by corrosion, oxidation or contamination. •    Contact bounce possible due to shock & vibration. •    Generates electromagnetic interference (EMI) / radio frequency interference (RFI). •    Can be orientation sensitive.