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The non-periodic nature of the drop-outs is like what the industry experienced 30 years ago when a tech with a walkie-talkie portable radio stood next to, or in close vicinity of, a field transmitter. When the tech keyed the radio 'on' to transmit, an indicating transmitter would go wild...

The documentation for a free Modbus slave stack (for the AT91SAM ARM-based Flash MCU) http://www.atmel.com/Images/doc11098.pdf uses Lamesoft Modbus Doctor as an example of using a Modbus master/client to access the slave. The document has two screen shots of Modbus Doctor. The screen shot...

>Also how about the question when the alarm of transmitter triggers? I don't have a clue what temperature alarms your DCS triggers. I'm a temperature guy. Let me summarize what the situation appears to be at this point. 4 indicated temperature signals fault, drop out at the same...

The FC-11 4-20 mA Isolated Signal Conditioner (at the link provided) will work in this situation. I agree with Mr. Mostia, it's good practice to always use isolated inputs. It also pays to use temperature transmitters that are isolated. Lots of vendors have similar offerings. I...

You might want to check and confirm that the transmitter is not square rooting the signal AND the DCS is also square rooting the transmitter's square root signal. It's been known to happen more than once.

Adding the additional 4-20mA signal exceeded the common mode rejection ability of the analog input card. You've created a ground loop by adding a signal whose reference ground is at a different potential than the original signals. A mild ground loop appears as an offset or noise. A...

It isn't clear whether only one of 8 points has the drop out problem, or all eight. If all 8 there's some common mode failure associated with all 8. I'll assume that there was only one point going bad, and the replacement transmitter is using the same DC power supply, wiring and receiver...

> Alternatively, Have you seen problems with cables in the past? Yes, corrosion in pH cabling can be a problem. Increased resistance will definitely affect a relatively low voltage high impedance pH signal. It's one reason for using a pH transmitter, but corrosion problems on the...

> can I connect the 4 wires from each RS-485 Modbus slave device in parallel > and then send it to Modbus Master RS-485 (DCS)? Parallel? Yes, but it depends on whether the RS-485 connection on the DCS side is 4 wire or 2 wire. If it is 2 wire on the DCS end, then you convert the 4 wire...

Welcome to Control.com Substitution with a known good probe and running a cal check is a good troubleshooting technique for checking the analyzer. You did not mention what pH value you read when you connected the pH probe to the 2nd analyzer, only that it was "acceptable". Given that a...

It seems that the statement below is the governing rule for how the SHJ S6889 serial server operates: "If the device ID not match local address or 255,then S6889 will reorganize the data according to modbus protocol, send out through zigbee or RS485 port. If register 7 is 6889, then...

A colleague calls them - Mules (packs the bits and carries them) - Rules (protocol, who talks, who listens, error handling) and - Tools (application level that deals with the data)

1) >CRC The Modbus over serial line V1.02 spec says the RTU frame has the CRC low byte first, then the high byte. (page 13) Lammertbies calculates B56F for 01030442c80000 in CRC-16 too. http://www.lammertbies.nl/comm/info/crc-calculation.html For B56F, which is low, which is high...

Assuming they all talk Modbus RTU (or all talk Modbus ASCII), yes. Usually a single USB-to-RS485 converter is used on a master, like a PC. Multiple slaves on one network is called multidrop. It is usually wired (+) to (+) to (+) , (-) to (-) to (-), or A to A to A, B to B to B...

94 pages of Executive Summary type data and it's in the public domain: TM 5-601 TECHNICAL MANUAL SUPERVISORY CONTROL AND DATA ACQUISITION (SCADA) SYSTEMS FOR COMMAND, CONTROL, COMMUNICATIONS, COMPUTER, INTELLIGENCE, SURVEILLANCE, AND RECONNAISSANCE (C4ISR) FACILITIES...

A relatively common statement in a spec covering instrument installation and commissioning is "Local indicating instruments shall be readable from where the related equipment is operated or from where the primary instruments are to be tested or calibrated." So you'll find local indicators...

1). Control and Protection of hydroelectric power plant http://www.kelm.ftn.uns.ac.rs/literatura/pdms/ControlAndProtectionOfHydroElectricStation.pdf or here: http://tinyurl.com/mlzlzhp 2). Subscribe to HydroWorld.com magazine http://www.hydroworld.com/topics/instrumentation-controls.htm

A variety of instrumentation and control training setups http://dacworldwide.com/product/detail/94 http://www.rib.se/html/products.html

One meaning of TIC is Temperature Indicating Controller. What that means for the panel at your company, I don't know. Ask your colleagues.

For instrumentation, Tony Kuphaldt's pdf book covers a lot at a practical level, and for cost (free), you can't beat it. http://www.ibiblio.org/kuphaldt/socratic/sinst/book/liii.pdf