How to create a -10...10V signal from a 24VDC to control prop valve with a joystick (potentiometer)

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emiller233

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pittsburgh, pa
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Controls-Automation engineer
we have a project that has existing proportional valves and joysticks that they're using. The customer wants to eliminate the controller/driver module and just use a proportional valve with Onboard Electronics.

so my question is how do i create this signal/voltage from just a 24VDC power source?

here is their existing joystick setup they're using for the -10...10V signal. I don't know the ohms of the joysticks yet
Capture10.JPG


data sheet for prop valve:

Capture11.JPG
 
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Go to Digikey, Mouser, or similar electronic supplier web site and order a DC-DC converter brick.
 
I understand the goal; done the same thing many times. BoschRexroth, the valve manufacturer, offers several modules that use +/-10V internally, but it looks like none today bring that out to the user. Look at their VT-SWMA and VT-SWMAK products. Their competitor EatonVickers EE-PAM series of cards have the output. My customers have bought a card from eBay and used it for JUST the power supply. I've not looked at Parker's offering in a few years.

If you can use 120 input, Acopian offers their relatively inexpensive 10EB series in 240, 400, 750, and 1000 mA. Almost certainly the 240mA is plenty. I've had these used successfully.

The REAL problem is getting a relay to reliably switch these signals. Many work for a "WHILE". Check specs for what the manufacturers call "dry circuit switching". With typical valve input Z over 10k (47k is most common IME), the contacts are switching 100 MICROAMP maximum. A-B, SquareD (Schneider) are honest if you dig that their reeds won't even be reliable in this service. The old P&B ice-cube relays with "crossbar" contacts are what you want.

Before retirement, this was my bread-and-butter; PM me if you want to discuss further. I'm in Greenville SC.

George
 
GeorgeB said:
I understand the goal; done the same thing many times. BoschRexroth, the valve manufacturer, offers several modules that use +/-10V internally, but it looks like none today bring that out to the user. Look at their VT-SWMA and VT-SWMAK products. Their competitor EatonVickers EE-PAM series of cards have the output. My customers have bought a card from eBay and used it for JUST the power supply. I've not looked at Parker's offering in a few years.

If you can use 120 input, Acopian offers their relatively inexpensive 10EB series in 240, 400, 750, and 1000 mA. Almost certainly the 240mA is plenty. I've had these used successfully.

The REAL problem is getting a relay to reliably switch these signals. Many work for a "WHILE". Check specs for what the manufacturers call "dry circuit switching". With typical valve input Z over 10k (47k is most common IME), the contacts are switching 100 MICROAMP maximum. A-B, SquareD (Schneider) are honest if you dig that their reeds won't even be reliable in this service. The old P&B ice-cube relays with "crossbar" contacts are what you want.

Before retirement, this was my bread-and-butter; PM me if you want to discuss further. I'm in Greenville SC.

George
Click to expand...
thanks!!, i will take you up on that option. PM sent
 
GeorgeB said:
... The REAL problem is getting a relay to reliably switch these signals. Many work for a "WHILE". Check specs for what the manufacturers call "dry circuit switching". With typical valve input Z over 10k (47k is most common IME), the contacts are switching 100 MICROAMP maximum. A-B, SquareD (Schneider) are honest if you dig that their reeds won't even be reliable in this service. The old P&B ice-cube relays with "crossbar" contacts are what you want.
Click to expand...
It seems like MOSFET analog transmission gates would be ideal for such an application, but I don't know if there are any available that are packaged within an industrial module. This integrated circuit would fit the bill:

www.analogictips.com

Analog multiplexers capable of switching signal voltages up to 36 V

Diodes Incorporated announced the introduction of the PS508 and PS509 analog multiplexers that are capable of switching signal voltages of up to 36V in an
www.analogictips.com www.analogictips.com

There are MOSFET relays from OMRON and others, but with a quick glance I didn't see any that would be appropriate for -10V to +10V analog signals.
 
PCB mount small signal relays are widely available and are pretty cheap. Socket mount ones are available but are rather expensive.
 
Given that the valves can either take a +-10V signal or a 4-20mA signal, you might consider putting a pot to 4-20mA converter at each joystick, and switching that.

My understanding is that 4-20mA is significantly more noise immune and also avoids the 'dry contact' problem on the relays.

(Note: not my area of expertise, GeorgeB is the expert!)

-Jon
 
I am no expert here either, but assuming the pots are connected to the -10/+10 supply at each end, the null position of the pot is zero and is failsafe in the event of a broken wire or similar failure. With the current loop input the null position of the pot would be in the middle of the current range no?
 
Todd0x1 said:
I am no expert here either, but assuming the pots are connected to the -10/+10 supply at each end, the null position of the pot is zero and is failsafe in the event of a broken wire or similar failure. With the current loop input the null position of the pot would be in the middle of the current range no?
Click to expand...
Yes, but ... details ... most 4-20mA devices regard signals much below 4 as a fault and still center. I've never used this product line in 4-20mA and DO NOT KNOW. If that matters, get information from a reliable source, IN WRITING. I have been in sales organizations, and would not rely on their outside force much. I know how the bipolar commanded ones work.

I do not like 4-20mA for bidirectional anything where 12mA is standstill. BUT, it is occasionally used.
 
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