Module with isolated analogue inputs having low leakage current
A module with isolated analog inputs for a programmable controller, the module including plural input pathways that are each isolated with aid of at least one optical isolation static relay controlled selectively with the aid of a controller. The module further includes a multiplexer including plural channels each controlled to open or to close, a channel of the multiplexer being placed in series with an isolated input pathway of the module.
1. A module with isolated analog inputs for use with a programmable controller, comprising:
a plurality of input pathways that are each isolated by at least one respective of optical isolation static relays controlled selectively by a first controller, wherein each pathway passes a respective signal;
a multiplexer including a plurality of channels including one respective channel for each of the plurality of input pathways, that each include a respective breaker controlled by a second controller to open or to close, wherein each respective channel of the multiplexer receives a respective signal passing on a respective of the pathways, and outputs a selected of the received signals, and the second controller controlling the multiplexer is coupled to the first controller controlling the optical isolation static relays so as to synchronize opening/closing of the plurality of input pathways, by controlling the respective plural isolation static relays, with opening/closing of a respective channel of the multiplexer, the multiplexer further including at least one channel employed to carry out an autocalibration including a channel routing a voltage reference, and the multiplexer further configured to short-circuit its input, for the autocalibration; and
an analog-digital converter connected to an output of the multiplexer, wherein the analog-digital converter receives the selected signal output from the multiplexer.
2. A module according to claim 1 , wherein each input pathway is isolated by two optical isolation static relays arranged in series.
3. A module according to claim 1 , wherein the multiplexer is a low-voltage analog multiplexer.
4. A module according to claim 3 , wherein the multiplexer is a low-voltage analog multiplexer with a supply voltage of approximately thirty volts.
5. A module according to claim 1 , further comprising a second controller to selectively control each breaker of the multiplexer.
6. A module according to claim 5 , wherein the second controller of the multiplexer is coupled to the first controller of the optical isolation static relays.
7. A module according to claim 1 , wherein the multiplexer comprises eight channels.
8. A module according to claim 1 , wherein the multiplexer comprises a channel routing ground.
9. A module according to claim 1 , wherein the multiplexer comprises a channel routing a power supply voltage.
10. A module according to claim 1 , wherein the multiplexer allows less leakage current than the optical isolation static relay.
11. A module according to claim 1 , wherein the plurality of input pathways comprises greater than 4 input pathways.