Internet PLC Forum

We currently have two T100MD-888+ in the field ( Oilfield Service application in Northern Alberta, Canada ) that are mounted in a sealed Dicast Aluminum cases, and carried on the Service Rigs.

The units have the more expensive Industrial temperatutre rated  CPU Chipset, and in our case a 16x2  -20 deg C rated LCD.

For the LCD, we had to add a negative bias supply for contrast control

( the T100MD-888+ only has a positive supply bias for the contrast on the LCD)

We used one of the Analog inputs on the T100MD-888+ to act as a bang bang type thermostat for a heater we created using 39 , 150 ohm resistors, placed on the PCB that supports the LCD.

We tested the The T100MD-888+ at -15 Deg C. in a freezer. No issues so far with the PLC, the only thing we have to do at -20 is allow the LCD to heat up for 4-5 minutes, so that we can get a better display reponse to the changing values.

We are currently preparing two more of these systems for the field.

The T100MD-888+ is a good unit for it's price, but I would like to see a bigger brother, that has more speed, larger memory capacity, and 12 bit A/D.

Come on Tri-PLC, You can do it ....

I have just received r48 Low temp CPU's to replace the r47's that I have. I will test these over the next week, to see if the RTC remains correct, and does not revert to 1/1/1998.

For curiosity sake, what changes were made to fix the problem?

Are there any other changes made, or added functions, for the r48 revision?

Your assistance is appreciated.

I ran two tests on the T100MD-888+ with MX-RTC installed. My system uses the HSC function with an optical encoder.

The first test was to power the unit, running the program without feeding it any encoder signals. The system was left 24/7 for two days and the clock operated correctly, changing at midnight to increment time and date, as well as being powered down, and back up with the correct time and date. ( Not a Low Temp rated CPU )

The second test, (done twice, once with the CPU that was shipped, and once with the low temp CPU) was with a signal generator running a simulated optical encoder input, as with the code above. The first day with the regular CPU clock incremented correctly, the second day the Low temp CPU arrived and was installed, Left overnight the clock reverted to 1/1/1998.

Powering the unit down, then back up again, 2 minutes later, produced a date of 8/9/1998 ( today being 8/19/2004 )

Conclusion, the reading of the clock, being interrupt driven, has an interaction with the HSC functionality

Both CPU's were r47 code.

If there are any tests that should be run, let me know.

I need to get this resolved.

This is my third T100MD-888+, the forth is on my desk, I believe the first unit I used ( which didnot have thid problem, I left it running with the simulator for close to a month ) had the r45 Code. Is it opossible to buy CPU's with the r45 code?

Your assistance is appreciated

Thankyou for your efforts.

I would like to connect a Quadrature encoder to a T100MD-888+,  say 128 PPR,  to HSC[1] and also feed one of the A or B signals into pin #5 as Interrupt Channel #3. This would allow me to synchronize reading A/D signals to every ( maybe ) rising pulse of the encoder.

The ISR ( Interrupt service routine ) would read 4 analog channels, and the value of HSC[1], do some processing, and then display the results on an LCD.

From an earlier discussion on timing, the moderator said

"The minimum scan time of the PLC is therefore = logic scan time (approx. 10us per word) plus I/o scan time (minimum 2ms)."

So if a program was say 1600 words long, I would expect a total period for one interrupt at 1600 x 10 us + 2 ms = to about 18 ms.

This would give me a maximum of say 50 interrupts per second.

What happens when the PLC see's incoming Interrupt pulses at a rate greater than 50 hz?

Is the interrupt input disabled when the ISR is processing, ( non retrigerable one shot equivalent ) and then re enabled when the routine is complete?

In other words, if the Interrupt is coming in at 150 Hz, will we still see a 50 hz. throughput, or will some error occur, and halt the PLC?

Your assistance is appreciated

I have had this phenomena happen on two T100MD-888+ with two different MX-RTC's.

The PLC is used in an application using an optical encoder to drive HSC1 and HSC2 . I am measuring position as well as velocity.In order to test my completed system, I feed a quadrature signal into the unit, and have the following code at 1st.Scan

SETSYSTEM 4,2 'set HSC2 encoder decoding to best for jitter
HSCDEF 2,2,2000000' set count to run Cust Fcn#2 at 27343 feet

' this is 128 ppr = to 1.75 ft
' set counter HSC[2] as a bi-directional quadrature encoder counter
HSCDEF 1,2,2147483647' set upper number to (2^31)-1 bits
'set counter HSC[1] as a pulse counter, no matter what direction
setlcd 0,1, chr$(12) ' hide cursor
J=0 'Used in Rod Rate Measurement using Rung Timing
SETBAUD 1, 4 ' SET COMM1 TO 19200, 8 , N, 1

Custom Function #2 is

' ZERO ENCODER COUNTER  SAVE DATA IN BATTERY BACKED MEMORY
IF HSCPV[2]=0  THEN GOTO @40 'Set Value of Encoder Counter to 0
ENDIF
IF V=0 THEN V=1
ENDIF
IF V>=3960 THEN V=1 ' LIMIT OF DATA FILE IN GROUPS OF 4, 4*990=3960
ENDIF
'AT 990 JOBS WILL START RECORDING OF DATA STARTING OVER AT DM[1]
DM[V]=DATE[2] ' MONTH
DM[V+1]=DATE[3] ' DAY
DM[V+2]=DATE[1] ' YEAR
DM[V+3]=HSCPV[1]*10/2399 ' SCALE IN WHOLE METERS
X=DM[3999] 'LOAD OLD TOTAL LOWER 16 BITS
SETHIGH16  X,DM[3998] 'LOAD OLD TOTAL UPPER 16 BITS
X=X+DM[V+3] 'ADD CURRENT CHAIN TRAVEL IN METERS
DM[3998]=GETHIGH16(X) 'WRITE UPPER 16 BITS OF TOTAL METERS TRAVELED
DM[3999]=X ' WRITE LOWER 16 BITS OF TOTAL METERS TRAVELED
DM[3995]=DATE[2] 'CURRENT MONTH FOR LAST TOTAL WRITTEN
DM[3996]=DATE[3] 'CURRENT DATE FOR LAST TOTAL WRITTEN
DM[3997]=DATE[1] 'CURRENT YEAR FOR LAST TOTAL WRITTEN
V=V+4

@40
HSCPV[2]=0  'Set Value of Encoder Counter to 0
HSCPV[1]=0  'Set Value of Encoder Counter to 0

If I leave the unit running continuously 24/7, typically I will see 10 resets per day, but when I return in the morning, the date has reverted to 1/1/1998. I have also had this happen when using On-line monitoring, where one instance it is displaying the correct date, then reverts to 1/1/1998.

Recently, I have run the system for 10 to 15 minutes each day, then removed power. The time and date settings are correct upon repowering the system. So the RTC is functioning properly when not powered.

Is there anything in my code that would lead to this date change?

Could it be a socket/MX-RTC pin  problem? If the PLC interrogates the MX-RTC every hour, is the communication specific to a particular pin or pins?

Do you have a recommended way of holding the MX-RTC in the socket, so that it won't come out? It slips in and out of the socket easily.

Your assistance is appreciated.

In a previous query, I asked what the effective input impedance was for the T100-MD-888+, and was told ( May 6 and 7, 2004 )

"there are already 2.2K resistor in series with all the AD1 to AD8 and AD1 to AD6 has 0.1uF capacitor in parallel to filter out high frequency noise on the analog inputs. AD7 (DA1) and AD8(DA2) do not have the 0.1uF capacitor."

As it turns out, the 0.1uf capacitance is presented directly to the DB15 pin, then the resistor is in series to the input to the CPU.

This effectively presents a capacitave loading to any source feeding it.

I have just run into this problem, with an op amp feeding the A/D inputs, and when connected to the T100MD-888+, the opamp( LTC1637) output showed an oscillation riding on a dc level.

I proceded to remove the CPU, and the problem persisted. Examining the T100MD-888+, and following traces, showed me that the 0.1uf caps were connected directly to the DB15S connector, then connected trough the 2.2 k resistor to the CPU. Shouldn't the resistor be presented first, then the cap for a RC filter?

The solution in my case was to install a 348 ohm resistor in series with the Op amp output.

So choose your op amps carefully, for use with the A/D inputs of the T100MD-888+. They require the ability to drive 0.1 uf capacitive load.

All comments are appreciated