| ??? 07/25/06 15:05 Modified: 07/25/06 15:06 Read: times |
#121027 - Some questions Responding to: ???'s previous message |
Prahlad said:
The circuit uses a constant current source built around LM358 and the voltage developed across the RTD is then amplified by using 3 Amp classic Instrumentation amplifier. Yes, you use a current source, but one that isn't properly suited to drive an external load. You can hardly protect this current source against ESD and similar. And with long cables it becomes unstable and oscillates! Also, I think the LM358 isn't precise enough. What precision do you need and what temperature range? PT100 shows a certain, well defined unlinearity. Do you want to linearize it by hardware (positive feedback methode) or by software? When driving a fast ADC, and this LPC2138 seems to contain a fast one, an OPamp with a fast settling time is urgently needed. The LM358 couldn't be fast enough. If we only had more details about the ADC... Kai |
| Topic | Author | Date |
| Reistor in series in signal from Amp to ADC. | 01/01/70 00:00 | |
| You forgot the other Question | 01/01/70 00:00 | |
| Read the app notes | 01/01/70 00:00 | |
| What ADC? What application? | 01/01/70 00:00 | |
| Re: Application. | 01/01/70 00:00 | |
| That's not good | 01/01/70 00:00 | |
| a much more elaborate protection scheme must be im | 01/01/70 00:00 | |
| Re: RTD & high voltage output. | 01/01/70 00:00 | |
| what about a zener across the RTD? | 01/01/70 00:00 | |
| Some questions | 01/01/70 00:00 | |
| ADC details? | 01/01/70 00:00 | |
| datasheet does not contain because | 01/01/70 00:00 | |
| ADC details still missing! | 01/01/70 00:00 | |
| Yes ADC details Missing,. | 01/01/70 00:00 | |
| That's what we need the details for... | 01/01/70 00:00 | |
| what detail? | 01/01/70 00:00 | |
| Analog input circuitry and timing diagram | 01/01/70 00:00 | |
| Forum Power. | 01/01/70 00:00 | |
| Link? | 01/01/70 00:00 | |
| Re Link. | 01/01/70 00:00 | |
| if you use them, sign up | 01/01/70 00:00 | |
Thanks | 01/01/70 00:00 |