Thermister electrical resistance values can range from 100 to 1,000,000 ohms at 25°C. The resistance change is approximately -4.4% per °C at 25°C. The large resistance change limits thermistors to narrow temperature ranges and low temperatures. However, in these situations, thermistors have greater accuracy and ambient temperature stability than RTDs or thermocouples. Lead wire can be as long as 1,000 feet without significant error.

Platinum RTD's electrical resistance values change approximately .385% per °C. The DIN standard element is 100 ohms at 0°C, showing a nearly linear change of + 38.5 ohms between 0 and 100°C. Platinum RTDs provide very good system accuracy at very low temperatures to 1000°F. Two wire RTDs have significant errors when over 10 feet long. However, these errors can be eliminated by using 4 wire RTDs.

Thermocouples re constructed of two wires of dissimilar metals that generate .05 MV per °C at the "hot" junction. The "cold" junction must be maintained temperature constant by electronic means to avoid signal errors. Low signals and linear complexities make system accuracy and integrity difficult. However, thermocouples respond to temperature changes very quickly, are virtually impervious to vibration or other mechanical conditions, have a wide range and high temperature capability.

Adaptor Plates for Mounting Smaller Size Controls in Larger Openings

PMAE-1: 1/4 DIN opening to 72MM PMAE-2: 1/4 DIN opening to 1/16 DIN      PMAE-3: 1/4 DIN opening to 1/8 DIN

PMAE-4: 1/8 DIN opening to 1/16 DIN PMAE-5: B/C 520- to 1/8 DIN PMAE-6: 72mm opening to 1/16 DIN

Other size adaptors available­Consult Ogden