According Watlow SD brochure : "Single universal input, up to three outputs" in the middle of page three, right column, below the table.

I'm guessing that PID Kits wires their system so the steam switch turns on the SSR and the alarm level trip kills the feed to the SSR, regulating the boiler at the alarm level.

I used a TC.
We use the AST pressure sensors in my day gig.

Nice TC mount, neat and solid. You must be right with the SD3C, I wonder if it's a viable solution

As for the AST sensors, I have failed to find one that works over 85°C so I guess it is a tad low for the inside of a boiler.
The one I have found is rated until 105°C which also seems low to me. Any idea Ian ?

I may have been wrong on the AST in the high temp application. I'll have to check with mfg on Monday to see what we use. They keep me locked in a room, poke wires through the wall and say "Measure this!"

another_jim wrote:At $200, the sensor should be putting out a standard controls signal, either 4 to 20mA (1 to 5 volt) or 0 to 10 volts. If it isn't, you are getting royally ripped. These standard signals work with every PID controller, including the 1/32nd DIN Fujis.

Most sensors that say "4 to 20mA output" still require a 24vdc power supply in the circuit so they can generate a signal. For home use, this power supply can be cheap, but it's still an additional piece of hardware.

As you say, even the least expensive Fuji accepts a 4-20 input, but the ultra-cheap Aubers, for instance, don't.

matthyx wrote:As for the AST sensors, I have failed to find one that works over 85°C so I guess it is a tad low for the inside of a boiler.
The one I have found is rated until 105°C which also seems low to me. Any idea Ian ?

The 85°C rating isn't really a problem, in my experience. You don't screw the sensor directly into the boiler. You locate it a short distance from the boiler, connected via a small diameter (ie, 3-4 mm OD) "capillary tube." The tube has several coils in it to trap condensate (as in the picture at the top of this page,) and the sensor will stay well below 85°C (but of course you should place it in a relatively cool area of your machine).

matthyx wrote:You must be right with the SD3C, I wonder if it's a viable solution

Depends on what you want to do, and how your machine is wired now.

Machines with dual-use boilers are generally wired so that the steam switch simply bypasses one of two series thermostats. So the stock wiring in the machine does most of the heavy lifting when it comes to using an alarm output as a steam setpoint.

Machines with single use boilers (e.g. HX, double boilers) probably lack the switch and wiring you would need to exactly duplicate what we do for steam control on single boiler machines.

But if nothing else, you could add a mini SPDT switch to select the DC- signal from either OT1 or OT2, and then feed it to the SSR. This would effectively give you 2 setpoints.

Jim

Hi guys,

Matt have you actually finished this 'project' and switched to a pressure transducer?

I have a TC (Omega) and a compression fitting for it (Swagelok) and I was planning to install it this week and use a Fuji PID to control the pressure in the boiler, but I also have a pressure transducer and could use that instead to keep the pressure at a (fairly) constant level. The only problem with this approach is the 24VDC power supply and fitting it inside the machine. One idea I had was removing the pressure stat completely and fitting the pressure transducer on the pipe that currently connects it with the boiler.

Andy have you got something similar, or are you using a TC-based approach?

Regards,
dsc.

I believe Andy is using a Speedster-based approach...

dsc wrote:..only problem with this approach is the 24VDC power supply and fitting it inside the machine.

There are umpteen wall wart solutions for a 120v/24VDC supply.
220v/24VDC are a bit scarcer :
http://www.ballicom.co.uk/audio-visual/ ... 88770.html

It's simple enough to solder a length of wire to the input terminals using and protect with a couple of layers of heat shrink. Bed the unit on the base of the machine with a heat sink compound and anchor in place with RTV silicone. As long as the unit is protected from spray, it should last a reasonable while. I have a 120/12 adapter in the HX machine and it's still fine 2+ years later.

Hi guys,

when talking about fitting problems I had the PT fitting on my mind, sorry if I wasn't clear. The reason for this is that because it has a 1/4" BSP male thread and almost everything inside the Elektra is 3/8". In addition I can't mount the PT directly on top of the boiler as it will get too hot and I can do that with the TC.

So it's either mounting it were the pstat is, or adding a 3/8" female compression fitting to 1/4" female threaded fitting pipe and installing the PT at it's end. Of course I can always use the TC and not bother at all.

As for the power supply the PT can ran from 8-24VDC and I already have a small 9V plug-in power supply, so it would be a simply matter of adding a few additional cables. Or as you say buying a small PSU and mounting it inside or near the machine.

Regards,
dsc.

cafeIKE wrote:I may have been wrong on the AST in the high temp application. I'll have to check with mfg on Monday to see what we use. They keep me locked in a room, poke wires through the wall and say "Measure this!"

You can protect the sensor by installing a coil of small diameter tubing between the sensor and the boiler. It's pretty standard practice for gauges and transducers on high-temp systems. You need to take care that there are no low spots in the coil that can collect condensed water. Otherwise no worries.

-Greg