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potential free contacts Contacts can be potential free in a standalone device, but for any means of control some voltage/current has to be present in order to sense the presence or absence of the voltage/current. So some voltage has to be applied to your 'sensor' contacts. 24Vdc is...

The analog signal, 4-20mA, is used worldwide because - it is simple and rugged - in its 2 wire, loop powered form it gets its power over the same wires as the signal - in its 2 wire form, it can be designed for Intrinsically Safe approval for use in hazardous areas, which allows...

Thanks for the excellent review. I'm going to get one just to try it out.

The loop powered isolators I'm familiar with scavenge power from the loop power supply (on the input side) to drive their own electronics and the loop current on the output side. If it were me, and I had a loop powered isolator lying around, I'd try it. force the source to max at 20mA and see...

Either there's a delta P and flow path so the meter is indicating true flow or there's true zero flow and the meter is falsely indicating flow. Since I've seen numerous examples of true flow when the pump is off with low flow sensitive clamp-on transit time ultrasonic flow meters, I tend to...

Ans: No. The solution Mr. Myres recommends is exactly what the alarm input board spec calls for - dry contacts. The alarm board design allows for a universal solution with practically no knowledge of electronics: dry contacts. Relay contacts are dry contacts as long as you don't connect any...

If you're a newbie and you're using the word 'hysteresis', you must have picked it up from something involved with this controller, so I'll propose that you have an on-off pressure controller. Every controller has a setpoint, which is the pressure value you want the system to be. The...

If you connect a HART communicator to a HART transmitter in a point-to-point current loop, the transmitter does what is always does - it converts the primary variable to a 4-20mA value on the current loop. - it responds to request(s) from the HART master, the HART communicator, for HART...

Unitronics issue with comm retries? RS-485 reflections from cabling's impedance mismatch? I notice the Hitachi uses an "RS45 modular jack" (apparently an an RJ45 connector carrying RS-485). Hitachi provides no internal termination resistors. Did you split apart the CAT cable to...

Sometimes you gotta bite the bullet and buy the book and you find out it pays for itself 20x over again. I'd recommend "Practical SCADA for Industry" by David Bailey and Edwin Wright. It answers the questions you're asking.

Do not locate the high and low side taps/ports at the 'top' of the pipe; do not locate them at 12:00. Instead, locate the taps/ports at 3:00 or 4:00 on the pipe circumference in order to avoid air/gas in the impulse lines. Probably be a good idea to use a 5 valve manifold so that you...

Valves are machined chunks of metal or plastic that don't talk Modbus. But the positioner or actuator that drives the valve might talk Modbus. A Google search for valve actuator Modbus will bring up a number of hits for actuators that talk Modbus. I suspect you're looking for a...

I could not enable a channel on an ISA100 wireless field transmitter until I had put the device into Out-of-Service mode (OOS). It would not accept the change while in operation. It might be something similar for your FF situation.

I know a number of controls guys who have programmed a PLC to run a motorized valve, but there are relatively inexpensive modules that take a linear voltage or DC current signal (like 4-20mA) and output the control signals to the actuator. http://api-usa.com/valve_positioner.php

The principles of operation for Fireye's UV flame scanner are explained in the opening paragraph: http://www.fireye.net/pdf/CU-22.pdf An amplifier and flame safety controller are typically separate electronic modules.

Siemens has a single channel ultrasonic level unit, the LUT400, which I saw a month or two ago. Its 4-20mA output is a new design; it can be either an active output, powered by the LUT, or a passive output, powered by an external DC power supply. The Siemens guy was with the local rep...

The first thing that comes to mind when you write, "When I try to poll input registers" is whether you mean that you are polling 3xxxxx input registers with function code 04. Does the Gateway support Modbus data on input registers? The Wireless HART gateway I saw put data into Holding...

1) A datum is missing - what is the expected DP range? It's a filter application, but is the expected DP across the filter 0.1 bar, 1 bar or 10bar? Is "dirty pressure drop bar VTA" supposed to mean something in this regard? It means nothing to me. 2) The pressure is getting up there...

Some comments on RS-485 or converters 1) I never use a port powered converter on a laptop because the serial port is not likely to supply sufficient electrical power for reliable use. Even on a desktop PC I will power the converter. 2) The labeling of RS-485 lines is all over the map...

Maybe you'd want to take some measurements, make a drawing and post it on site where it could be accessed? There's not a lot of incentive to pursue a VERY specific diverting valve only knowing that it's a diverting valve.