| ??? 11/17/13 19:13 Read: times |
#190149 - test bench vs field design Responding to: ???'s previous message |
Raghunathan said:
This whole requirement arose beacuse I was trying to verify a data acquistion channel meant for a 2 wire loop powered transmitter. In the absence of a calibrator I replaced the transmittter with a combination of 5k/1.5W potentiometer + 1kOhm series resistor. It did the job - quick and dirty - but I was not at ease about the potentiometer when near the 20mA setting. [ loop was powered by a 24V dc source ]
If it is a test-bench use only, the bar is rather lower than for something that has to work z000 hours. One aspect of wiper current, will be noise degradation, important in field-lifetime design, but a don't-care on a quick test bench. The other detail with POTs is they tend to have a mW/mm rating - ie the element here will manage 1.5W across the whole material, but that means 50% in variable resistor mode, is 750mW if the power density is kept the same. Since you know 24V and 20mA, another approach is to use fixed resistors to get within say 20% of your target and then pass only the 20% needed thru the pot. |
| Topic | Author | Date |
| Power rating of potentiometers | 01/01/70 00:00 | |
| Not the point | 01/01/70 00:00 | |
| show me such | 01/01/70 00:00 | |
| (was) incorrect | 01/01/70 00:00 | |
| not your average "pot" | 01/01/70 00:00 | |
| Specs that are not normally told.. | 01/01/70 00:00 | |
| power | 01/01/70 00:00 | |
| test bench vs field design | 01/01/70 00:00 | |
| That was kind of my point | 01/01/70 00:00 | |
| pot limits | 01/01/70 00:00 | |
| While I don't disagree ... there are different failure modes | 01/01/70 00:00 | |
| Bourns says: "yes." | 01/01/70 00:00 | |
| Tesla says: no | 01/01/70 00:00 | |
| cermet or wirewound | 01/01/70 00:00 | |
No big difference, if it all | 01/01/70 00:00 |