Tag Archives: history

Application information for Allen Bradley resistors

Allen Bradley resistors are one of the best sellers on the West Florida Components web site with good reason.

The following information has been compiled to aid in the everyday selection and application of Allen-Bradley hot molded resistors. The statements should be helpful in evaluating the use of all types of AB hot molded resistors in broad general terms, and are not to be interpreted to be precise or exact.

A comprehensive list is made of the standard normal resistance values in their available tolerance categories, the rated continuous working voltages for all hot molded types, the part numbers, and color codes – all information provided for all values from 1 ohm to 100M ohm, taking into account the available range of values for each type (as of 1985).

Allen Bradley Resistors

Allen Bradley Resistors

1 – Low value resistors exhibit less change due to humidity, temperature and voltage than high value resistors.

2 – Resistance changes due to increase in moisture content are always positive.

3 – Resistance changes due to humidity are temporary, and, in the case of Allen Bradley resistors, are reversible.

4 – Change of resistance which has occurred due to humidity may be essentially eliminated by conditioning the resistor at 100°C or by dry storage.

5 – The effects of humidity may be minimized by operating the resistor with as little as 1/10 rated wattage load.

6 – Resistance change due to load life is permanent and usually ultimately negative.

7 – Resistance change due to load life can be minimized 1% – 2% in many thousands of hours by 50% derating period. The same result can be attained by limiting the maximum operation surface temperature of the resistor underload to 100°C. Permanent resistance changes as a result of storage of temperatures below 100°C are negligible, even for extended time periods.

8 – Resistance change due to soldering is positive and may be permanent if the resistor has excessive moisture present in its body. It can be greatly minimized if resistors are dry at the time of soldering.

9 – The temperature characteristics of Allen Bradley resistors is positive above +80 and below -10.

10 – The temperature characteristics of Allen Bradley resistors is negligible from -10°C to +80°C.

11 – The voltage characteristic (negative) and the temperature characteristic (positive) of Allen Bradley resistors tend to cancel one another in an Allen Bradley resistor in an average operating conditions, where both significant voltage and elevated temperature are present.

12- The heat sink to which a resistor is connected affects its rating. Resistors operated in multiple should be derated unless adequate heatsinks are provided.

13 – The quality and reliability of Allen Bradley resistors is the same for, and independent of, any resistance tolerances shown on the resistor.

14 – Years of accumulated experience have shown that Allen Bradley hot molded resistors are unequaled for uniformity, predictable for performance, appearance, and freedom from catastrophic failure. Allen Bradley resistors are made by an exclusive hot molding process on automatic machines developed, built, and used only by Allen Bradley. There is such complete uniformity from one resistor to the next, million after million, and long term in-circuit performance can be predicted with usable accuracy. When used according to published ratings and recommendations, Allen Bradley hot molded fixed resistors will not open circuit nor exhibit erratic changes of resistance value. They are probably the most reliable of all electronic components.

This information was taken in part from the Allen-Bradley corporation reference book dated 1985.

Op Amps – Then and Now

Op Amps – Then and Now

Op amp is the commonly used name for operational amplifiers, which are widely used electronic components. Op amps are often seen on many surface equipment designs and logging tools.

The name ‘operational amplifier’ comes from the use of such high gain amps in performing mathematical operations for analog computer operations and is said to have been coined in 1947. A lot of study was done in the field and the initial operational amplifiers, based on vacuum tubes, were a result of the research done in Bell labs. By 1960’s, vacuum tube op amps had given way to solid state devices and hybrid operational amplifiers were entering the scene.

The first IC operational amplifier was developed in 1963 by Bob Widlar and was called Fairchild µA702. It was not a success because of a number of bugs. But Widlar’s next design, which was the µA709, was hailed as milestone in design. A number of designs followed including the very popular µA741. A number of precision op amps like OP7, OP27 and OP37 are commonly used in logging electronics.

In the initial days, these electronic components were based on NPN bipolar process and because of the slow PNP transistors of the time; the speed of the amps was limited. The LM118/218/318 model tried to solve the problem but did not meet with much success. The only fast IC op amps were the ones owned by Harris, the HA2500 as well as the HA2600, and were quite popular despite their high cost.

FET input operational amplifiers though highly advantageous in downhole tool applications, did not enter the scene due to engineering problems. However with the introduction of the ion implantation process in 1974, their manufacture became possible and the LF155/156/157 series was introduced by National Semiconductor, and OP15, OP16, and OP17 by PMI. The TL06x, TL07x, and TL08x models introduced by Texas Instruments (TI) in 1978 went on to become industry standards.

The CA3130 employing a P-channel MOS input with a CMOS output, set the stage for CA3140 having a MOSFET input and a bipolar output which caught the eye of many logging tool companies. This model has many advantages including good bandwidth and military temperature range, and continues to be used and manufactured even now.