I'm an engineering designer formally trained in mechanical engineering, with experience in digital electronics (although never formally trained in electronics), and now have a need to employ an instrumentational amplifier in a loadcell application. Having just swated up on basic op amps., I have a couple of questions.
1. I am given to understand that when connecting the inputs to a loadcell (and, in particular, a thermocouple) I need to provide a bias current path for one or other of the inputs to earth or one of the supply rails. However, as the device in question employs FET (as opposed to bipolar) inputs, do I not need to concern myself with providing a bias current path ? If so, what resistor value should I use to earth ? (the loadcell has an impedance of 1K across the bridge and will be excited between 4.7 - 5.6 V via a resistive potential divider arrangement, between the + and - power rails with a zener across the excitation input to stabilize the voltage).
2. I am currently running off supply rails of + and - 12.3 V and am only getting an output voltage swing of +/- 10 V. If I have interpreted your data correctly, an output swing of up to +/- 12 V is possible; will I achieve this if I increase the supply rail potentials by a few volts ?
I apologize if this is basic electronics and would thank anyone for their kind assistance.
Many thanks, Gustavo, for a very detailed answer which is extremely helpful.
I'm just returning to engineering after a very long break and have lost touch with a lot of technology and have just started trying to develop a range of products.
The AMPO2 rather chose me, being cheaply available on eBay, as I wasn't looking for anything particularly accurate provided the drift was low. However, having looked as various distrubutors prices (bearing in mind that I hope this will result in a batch production project) I can see that I can get equally good deals on superior inst amps without having to rely on an inconsistent supply source.
I'll certainly take a look at the link you have provided.
Many thanks once again.