Temp Sensor IC study
T Chap
Posts: 4,223
Why does temperature affect current sensing?
There is a 393 comparator that gets an output from a differential amp that measures current into the motor driver PCB on one input, and a voltage via the Prop DAC on the other input for setting a trip point. This way I can set a 'trip point' level with software for over-current to trigger something on the Prop.
The current sensing varies by temperature. When the temp changes by a few degrees, the current sense software trip point gets out from where I set it originally (the sensitivity to motors load). Basically I am setting the current trip point very tight for minute detection of motor load.
If I set the office AC to 70, and set the trip point where is works nicely and very sensitive, then set the AC to 65 and await a bit, the trip happens when I don't want it too, in other words the trip is too sensitive when it gets colder. If I put a hair dryer on the motor driver PCB, within seconds the sensitivity becomes more like it was, but if I hold the heat there for a while, the system becomes not sensitive enough. So the hotter the temp, the higher I need to crank the DAC, the colder, the lower the DAC.
I have a MAX6634 temp sensor on the main board, and am trying to work out a method to bias the Prop DAC output level trip point to change with the temperature. Theoretically this should solve the problem right? The question is whether there is anything else that can be done. The sense resistor is a 2 watt wirewound 1ohm, with a precision differential amp. The system needs a consistent trip setting, to allow for warmer summer days if windows are open, and colder winter days.
Any suggestions appreciated.
There is a 393 comparator that gets an output from a differential amp that measures current into the motor driver PCB on one input, and a voltage via the Prop DAC on the other input for setting a trip point. This way I can set a 'trip point' level with software for over-current to trigger something on the Prop.
The current sensing varies by temperature. When the temp changes by a few degrees, the current sense software trip point gets out from where I set it originally (the sensitivity to motors load). Basically I am setting the current trip point very tight for minute detection of motor load.
If I set the office AC to 70, and set the trip point where is works nicely and very sensitive, then set the AC to 65 and await a bit, the trip happens when I don't want it too, in other words the trip is too sensitive when it gets colder. If I put a hair dryer on the motor driver PCB, within seconds the sensitivity becomes more like it was, but if I hold the heat there for a while, the system becomes not sensitive enough. So the hotter the temp, the higher I need to crank the DAC, the colder, the lower the DAC.
I have a MAX6634 temp sensor on the main board, and am trying to work out a method to bias the Prop DAC output level trip point to change with the temperature. Theoretically this should solve the problem right? The question is whether there is anything else that can be done. The sense resistor is a 2 watt wirewound 1ohm, with a precision differential amp. The system needs a consistent trip setting, to allow for warmer summer days if windows are open, and colder winter days.
Any suggestions appreciated.