Here is a list of conversion formulas and miscellaneous technical information. Please feel free to bookmark this page for your quick reference. It will be continually updated. Any suggestions will be appreciated.
Measure Cable Characteristics
HOW CHARACTERISTICS ARE MEASURED FOR Intercon 1 CABLES (sample)
- Characteristic Impedance TDR Single End – This test measures impedance of a transmission line using Time Domain Reflections. The equipment commonly used is a Tektronics 11801A Digital Oscilloscope. A signal is sent down the line, the reflected signal coefficient is recorded at a point 4.7 Ns down the length of the cable. The measurement is the reflection coefficient and is used to calibrate the impedance by use of the following formula.
|z=||1 + p
1 – p
|Where||Z = Impedance
R = 50 ohms
p = Reflection Coefficient
- Capacitance Single End – Using a HP 4262A Digital LCR Meter (or similar) single end capacitance is measured. Readings come directly from the meter.
- Conductor Resistance – Using the HP 4262A Digital LCR Meter (or similar), the resistance of a conductor is measured in a 1,000 ft cable. Max allowed based on cable requirements.
- Insulation Resistance – This measures the insulation resistivity using a Hypotronics HM3A Megometer (or similar).
Impedance is the total opposition in a system to alternating current. It is important to match a cableÕs impedance to the instrument or device being used. Due to low level power in electronics or communication devices, unmatched impedanceÕs will cause power or signal strength loses. Proper impedance matching allows for optimum energy transfer conditions. When testing the cables for impedance there will usually be a specific impedance value to look for with a tolerance of + or – a certain range in ohms. The value is determined from what the cable applications will be as well as what kind of transmissions into the cable are expected. Normally, Intercon 1 cable will have a tolerance of + / – 4 ohms. For some cables the tolerance is + / – 3 ohms.
Capacitance is a charge storing property of an element. In our case it’s the charge storing property of cables. Capacitance can affect the shape of transmitted signal waveforms. If the capacitance changes enough the results can be in the form of phase lagging, decreased amplitude, and/or signal filtering. Again when tested there will usually be a specific value with a tolerance range for the requirements which will be determined by the cable application.
Conductor Resistance is simply the resistance to current flow in the conductor. The higher the resistance the less conductivity in the wire. Maximum resistance is usually in ohms/1,000 ft.
Insulation Resistance is simply the resistance to current flow in the conductor. The higher the resistance the less conductivity in the wire. Maximum resistance is usually in ohms/1,000 ft.
General Coaxial Cable Data
Coaxial cable consists of a center conductor surrounded by an outer, tubular conductor, a dielectric that separates the conductors, and a jacket that protects the parts. The inner conductor typically is a solid or stranded wire while the outer conductor generally is a single – or double – braided shield or tubing.Similar to shielded wire in construction, the essential difference between coaxial cabling and shielded wire is that coaxial cable transmits a signal with as little loss as possible, with little or no distortion, and minimum radiation. In shielded wire, the shield is merely used to confine the signal or to screen it from external excitation: It does not have the controlled characteristics of coaxial cable. The four basic parameters of coaxial cable are:
Velocity of propagation
All are interrelated and depend on the properties of the dielectric and the cable dimensions. Additionally, when specifying coaxial cable, the voltage standing wave ratio (VSWR) and the dielectric constant must also be considered.
General Coax Connector Data
50 ohm vs. 75 ohm
Historically 50 ohm BNC connectors have been used with 75 ohm cable for analog video equipment with little distortion effect on the signal at frequencies below 300 MHz. However, digital signals in video applications have necessitated the usage of 75 ohm connectors with 75 ohm cable. Mismatched connectors cause attenuation of the digital signal resulting in slower rise time of square waves. This distortion of the signal can cause transmission errors.Also, impedance mismatched connections cause reflections of the signal returning to the source known as return loss. Often one mismatched connection will not have a noticeable effect on system performance, but multiple mismatched connections in the link between the source and destination have a cumulative effect causing possible distortion of the transmitted signal.As a standard practice, Intercon 1 uses only 75 ohm connectors with gold plated terminals (source Connex or Tyco) with 75 ohm cable.BNC Background: In the early 1940’s, it is generally agreed that a group of three individuals (Bayonet, Neill and Councelman) developed a new coaxial cable connector with the express purpose of providing a secure interface and an easy to use locking mechanism. These connectors were used to link equipment incorporating an electronic vacuum tube platform. The new connector was referred to as the BNC recognizing the origin of its development.
First Code Number *IP **Classifies Protection against Touch and Intrusion of Foreign Particles
|Code||Description||Level of Protection|
|0||No Protection||No protection against accidental touch of parts under power or moving or stationary parts.|
|1||Protection against large foreign parts||Protection against accidental touch of parts under power in large areas or internal moving parts. Protected against intrusion of particles larger than 50mm diameter.|
|2||Protection against medium foreign particles||Protection against accidental touch with fingers of parts under power or moving internal parts. Protected against intrusion of particles larger than 12mm diameter.|
|3||Protection against small foreign particles||Protection against accidental touch of parts under power or internal moving part with tools, wires or similar objects with thickness of larger than 2.5mm. Protected against intrusion of particles larger than 1mm.|
|4||Protection against grain-sized particles||Protection against accidental touch of parts under power or internal moving parts with tools, wires, or similar objects with a size larger than 1mm. Protected against intrusion of parts larger than 1mm.|
|5||Protection against dust deposit||Complete protection against accidental touch of parts under power or internal moving parts with tools, wires, or similar objects. Protected against intrusion of dust particles is not completely prevented, but dust particles can not deposit in such quantity that performance is compromised.|
|6||Protection against intrusion||Complete protection against accidental touch of parts under power or internal moving parts. Protected against detrimental dust deposition. Intrusion of dust is not completely prevented, but can not have a detrimental effect on the performance of the device.|
Second Code Number *IP **Classifies Protection against Intrusion of Water
|Code||Description||Level of Protection|
|0||No Protection||No designated protection.|
|1||Protection against vertical water droplets||Water droplets falling vertically onto the device have not negative effect.|
|2||Protection against oblique falling droplets||Water droplets falling at an angle of not more than 15° from the vertical onto the device have no negative effect.|
|3||Protection against water splash||Water, falling at an angle of no more than 60° from vertical have no negative effect on the device.|
|4||Protection against water spray||Protection against water spray.|
|5||Protection against water jet||Water jet from all directions has no measurable negative effect.|
|6||Protection against flooding||Water has no negative effect during temporarily flooding.|
|7||Protection against submersion||Water can not penetrate for a defined period and depth of submersion.|
|8||Protection while permanently submersed||Water can not penetrate for an indefinite period of submersion at a defined depth.|
Current Carrying Capacity of Copper Conductors
Current carrying capacity is defined as
the amperage a conductor can safely carry before melting occurs in the conductor and/or the insulation.
Conductor Size: The larger the circular mil area, the greater the current capacity. Insulation: The amount of heat generated should never exceed the maximum temperature rating of the insulation material. Ambient temperature: The higher the ambient temperature, the less heat required to reach the maximum temperature rating of the insulation. Conductor Number: Heat dissipation is lessened as the number of individually insulated conductors, bundled together, is increased. Installation Conditions: Restricting the heat dissipation by installing the conductor in conduit, duct, trays or raceways lessens the current carrying capacity. This restriction can be alleviated somewhat by using proper ventilation methods, forced air cooling, etc. Given all of the variables, no simple chart can be developed. This data is for reference only to be used when developing your basic requirements.