1. Will an API 4000 G work with an input temperature range of 1000 to 2000°F?
Yes, however to utilize the charts for selecting the switch positions in the field, we need to convert °F to °C. This would give 550°C to 1100°C which can be selected from the charts.
2. We have four of your API 4130 GL modules set for a K type thermocouple with an input range of 0-2000°F and an output range of 4-20 mA. For an input of 0°C, the outputs on all 4 units are calibrated to 4 mA. For an input of 2000°F, the outputs of all 4 units are calibrated to 20 mA. When the input is at 1000°F, the outputs of each of the 4 units is different (11.8, 11.9 etc.). Can better performance be achieved?
The linearity specification is ±0.5% of span which is ±10°F for a range of 2000°F. For an input of 1000°F, the output can vary from 990°F to 1010°F.
Also, output span / input temp range gives (20 – 4 = 16), 16 mA / 2000°F = .008 mA per °F for the entire range. For an input of 1000°F, the output can be in the range of 11.92 mA to 12.08 mA. You are getting 11.8, 11.9 etc. which are probably the variations in the accuracy of the four thermocouples, the extension wire, the thermocouple simulator, the multimeter and the wiring connections.
If you want API to verify this with our NIST traceable simulators just call customer service at 248-636-1515 for an RMA number. The API 4000 G is even more accurate which should be used for high precision applications.
3. Can the API 1200 G provide a setpoint of 7°C and a reset point of 6°C with an overall temperature span of 0-10°C?
No. The minimum span we can operate in is a temperature difference equivalent to 5 mV of output change from the thermocouple. For example, a type J will produce 0.000 millivolts thermoelectric voltage at 0°C and 5.268 millivolts at 100°C. Therefore, the minimum temperature span is about 100°C. For the set point at 7°C and reset point at 6°C, the thermocouple itself has enough of a variance (usually 5%) to it that its output will not be exactly the same. So, we can not guarantee the repeatability of the system to trip at 7°C each time.
4. What is cold junction compensation and why is it necessary?
Cold junction compensation is required for accurate temperature measurement when using a thermocouple. A thermocouple junction, created whenever two dissimilar metals are connected together (such as Iron and Copper-Nickel), produces a potential difference that varies with temperature. Thermocouples generate a millivolt signal which increases in proportion to the difference in temperature between the hot and the cold junctions. Thermocouple tables are based on a standard 0°C cold junction temperature. Instruments designed to read thermocouples have a temperature sensor at the instrument connection point designed to electronically correct the reading to the 0°C standard. A millivolt meter can’t be used to accurately read a thermocouple directly since it has no 0°C compensation. Additional connections with dissimilar metals create new thermocouple junctions also adding to the error if their temperature varies.
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