Internet PLC Forum

On our machine we have a couple of different 2-wire switches wired into T100MD888+ PLCs.  One has problems and one works fine.  Here are some specs:

Switch #1: Pressure switch (SMC part # PS1000)
Load voltage: 12-24 VDC (we're running at 24V)
Load current: 5-40 mA
Leakage current: < 1 mA
Internal voltage drop: < 5 V
On voltage measured at PLC input: 3 V
Off voltage measured at PLC input: 15.2 V

Switch #2: Proximity switch (SMC part # D-C73)
Load voltage: 24 VDC
Load current: 5-40 mA
Leakage current: not specified
Internal voltage drop: < 2.4 V
On voltage measured at PLC input: 1.6V
Off voltage measured at PLC input: 19.3V

Switch #1 is the one that doesn't work properly.  If I power up the PLC and the switch is already on (i.e. air pressure is on) the PLC reads the input as on.  If I turn down the pressure until the switch goes off, the input goes off as well (so far so good).  However, if I now increase the air pressure until the switch turns on, the input doesn't turn back on again.  The only way to get the PLC to read the input as on is to power up the PLC while the pressure is on.

I tried the two suggestions mentioned in this thread but neither achieved anything.

I know this really isn't a TriPLC issue but I was hoping you might have some insight into this since you are more familiar with the design of your PLCs.  Plus, you've been very helpful with questions like this in the past.

I'm having communication problems with a T100MD888+ PLC.  The TLServer keeps disconnecting with an error stating:

Bad Network Performance

Please check the following:

1. None of the slave nodes are sending data on RS485
2. Long network is properly terminated and biased

We have an ICP module connected to the RS485 port on this PLC and this is the first time we've done this.  We don't have biasing resistors on the port (simply because we can't add another power supply to our system) but regardless of the potential problems caused by that we are communicating with the PLC using the RS232 port.  Could communication errors on the RS485 port cause failures on the RS232 port?

I've implemented a jog feature in our 888 program by sending large values to STEPMOVE and issuing a STEPSTOP when the jogging is done.  However we recently uncovered a problem with this technique that somehow escaped our notice before.  If the speeds are too high suddenly stopping the motor with STEPSTOP results in the motor skipping a number of steps (due to momentum) which knocks the position off.

One solution is to limit jog speeds but this is very unsatisfactory since the speeds would be too slow to be useful in our application.

So consider this post an enhancement request for future versions of the Triplc firmware.  I'd like to either see some jog functions added (maybe even simplifying the use of an analog input for speed control) or at the least add a deceleration parameter to the STEPSTOP command where obviously a decel of "0" would make it work as it does now.

Does anyone have any ideas for interfacing a 50 ohm oscilloscope probe with a Triplc's analog inputs?  Maybe there's a signal conditioner or something that can be used?

edit: I didn't know if this should be in the General forum.  I figured here since it could be of interest to other Triplc users.

Are your PLCs manufactured lead-free?  We're hoping to start shipping machines to Europe and ROHS requires them to be lead-free.

We broke a voltage regulator off one of our MD888's.  The part # is KA7810.

The only place that sells these (that we frequent) is Mouser.  We'd like to order something from Allied since we already buy other stuff from them.  Is there another part we can use in place of this that might be more common?

Can I use the Triplc's (T100MD888+, specifically) PWM outputs as dimmers for halogen lighting?  Has anyone tried this?

A 24VDC, 50 Watt bulb will draw just over 2A at full on so it falls within the PWM output's capabilities.  

What about the concept of using PWM for halogen dimming?  Is this even a valid technique?  If so, what's the lowest frequency I can run the PWM at without the bulbs flickering or pulsing?  And can I drive the bulbs with the same power supply I use for the Triplc or is that a bad idea?

I know I can probably answer most of these questions experimentally (and I probably will) but I just wanted to be a little confident that I'm not going to fry a plc before I try it.