BX-08AD-3 Module Question

[RBPLC]

Scenario:
BX-08AD-3 Module attached at first slot on BX-DM1E-18ED23-D.
WX1 is off with WX2, WX3 and WX4 on. All analog inputs are setup such that:
Analog Input: 0-5, Enable Scaling: WX2 min = 0, WX2 max=32267, RX2 min=0, RX2 max=5. This is the same setup for WX3 and WX4. When I apply a process calibrator at 0VDC to the input I see 0 VDC +/- 0.003VDC. When I remove the process calibrator from the channel, Counts jump to about 4100 corresponding to 0.625 volts. This reading is the same when the terminal block is completely removed. What's the deal?

[BobO]

Scenario:
BX-08AD-3 Module attached at first slot on BX-DM1E-18ED23-D.
WX1 is off with WX2, WX3 and WX4 on. All analog inputs are setup such that:
Analog Input: 0-5, Enable Scaling: WX2 min = 0, WX2 max=32267, RX2 min=0, RX2 max=5. This is the same setup for WX3 and WX4. When I apply a process calibrator at 0VDC to the input I see 0 VDC +/- 0.003VDC. When I remove the process calibrator from the channel, Counts jump to about 4100 corresponding to 0.625 volts. This reading is the same when the terminal block is completely removed. What's the deal?

Are they disconnected? Voltage inputs are pretty high impedance and can float when disconnected.

[RBPLC]

Yes, they're disconnected completely when the terminal block is pulled out. The issue with this is that if you've got a sensor that comes unplugged or a wire gets cut for example, these inputs appear to float which could be bad news. 

[BobO]

Yes, they're disconnected completely when the terminal block is pulled out. The issue with this is that if you've got a sensor that comes unplugged or a wire gets cut for example, these inputs appear to float which could be bad news.

And that is why most use 4-20ma in industrial environments. If you don't mind a small loss of accuracy, add a 100k or 1M ohm resistor to ground. That should pull it to ground without disturbing the result.

[RBPLC]

4-20 sensors aren't always an option. I'm wondering if anyone else has ran into this and if there's a better option than jumping a resistor on a terminal block. What's the feasibility of adding a pull-down to the module?