RS232/RS485 COMMUNICATION SOURCE

[fifty60]

I have a power supply that I need to have shut down if my equipment experiences an alarm. There are no digital inputs on this equipment. There are RS232,RS485, and Ethernet communications ports on the equipment that I can use to shut down the power supply.

Does anyone know of a piece of equipment that when powered up will send out a communications signal over RS232 or RS485? I do not need the equipment to do anything else other than send out this single signal when it is powered up. My equipment can power up this module during an alarm, and when the module is powered it will transmit the shut down signal.

 

[GoldDigger]

"Communications signal"?
RS-232 is a character based serial communications protocol.
You give some status lines that could indicate a go/no-go signal, but on the data line you would need to send a coded message of one or more characters.
To do that you pretty much need a processor of some sort in the product. Not much of one though.
I am sure such products exist, and at a lower cost than a full PLC, but I do not have any references.

Tapatalk!

 

[gar]

140416-1612 EDT

fifty60:

There are devices that can do what you want. You need to provide more information on details of the required shutdown signal?

How serious is the result, if the shutdown signal is missed or contains errors, and then shutdown does not occur?
Can the RS232 hardware handshake signals be used to control shutdown?
How does the power supply get turned on?
Can you simply control the input power to the power supply?
Do you need to turn on the supply via the RS232 link?
For what else do you need to use the RS232 port?

.

 

[fifty60]

I actually only need a TTL logic signal to shut down the remote equipment. I do not have TTL voltage levels available, but I think all I will need is a 5V output power supply and a bifurcated gold plated relay and I will have what I need. Relay coil energized to allow the 5V hi signal, not energized to provide the 0V signal.

Would I have any problems with the 0V level being floating and not tied to ground? Can anyone recommend a better way to do this?

 

[drktmplr12]

I think we need a better idea of what equipment you have and what you are specifically trying to accomplish. Otherwise we cannot give you coherent direction based on fact. All we can do is speculate.

What we know:
1. You have a power supply and a piece of equipment.
2. You need to turn off a power supply based off of failure signal from a piece of equipment.

What we don't know:
1. What kind of signal is this failure indication? Dry contact?
2. Does this mysterious piece of equipment have a name/part #/model #?
3. What does it do? Does it control something?
4. How is the power supply powered?
5. How is the equipment powered?

 

[drktmplr12]

Would I have any problems with the 0V level being floating and not tied to ground? Can anyone recommend a better way to do this?

No it shouldn't be a problem because the relay coil doesn't care about the voltage relative to ground. To me, it seems like if you can shut down the existing power supply without losing the signal that turns on the proposed 5V power supply...that would be the simplest way to go if you insist on using TTL.

Why not just use the signal that turns on the 5V power supply to remove the line voltage from the existing power supply?

edit: disregard my previous post if it isn't relevant.

 

[gar]

140416-1933 EDT

fifty60:

Define exactly what signal you require at the device you want to control. A TTL signal means a lot, but TTL alone still means much lacking information (for example is the load of the input equivalent to a standard 7404 gate), and on the other hand it still does not mean much in your application.

You seem to be hungup on bifurcated gold contacts. If your power supply that is to be controlled has an actual 7404 gate as its input, then at the connector where this input exists is there possibly a +5 V pin. There is certainly a 5 V common pin. In many cases I have left a gate input float to get a logic 1 input, but that is not a good idea in your case for a number of reasons. I would like to see a 1 k pullup resistor to the +5 V supply. Note: if you have a standard TTL input, then most certainly there is +5 inside the power supply. You could even put the 1 k pullup inside the supply. Also there might already be an internal pullup. Measure the voltage from the input pin to its common. With a pullup then a simple 4N35 could be your isolated coupling.

.

 

[dereckbc]

This sounds pretty simple to me. All you need is a relay with dry contacts. NO and NC to flip anything on or off. I must be missing something.

 

[GoldDigger]

Well, if RS-232 control leads will be used, you need to supply + 15V and - 15V to be compliant.
You may be able to get away with +/- 5V, but 0 and +5 will often not cut it.

Tapatalk!

 

[gar]

140416-2037 EDT

fifty60:

Why did you ever bring up 232 in the original post when apparently from post #4 your input control is a binary TTL input?


GoldDigger:

+/-15 is not a requirement of RS232. +/-12 was also used as a standard, and more recently it is down to +/-5. Many so called RS232 receivers and drivers do not meet the standards for input threshold and deadband, and on output the current limit and slope specifications.

Some equipment was using just a transistor base-emitter junction as the input threshold mechanism with no feedback for hysteresis. Not very voltage tolerant. Some new input circuits have large input voltage limits, like +/-25 V, without damage.

The new +/-5 specifications will drive old original RS232 receivers, but the usable cable length might be reduced.

.

 

[fifty60]

Sorry about stating the RS232, it is a 168 page manual dropped on my lap and the first remote operation option I see is the DB-9 for the RS232. There is also a DB-25 titled "analog interface" that has a pin assigned for remote shut down of the power supply via a TTL signal applied to pin 22.

The is a +12VAPI on pin 1, but this is not the +5 volts I would need to send my signal to pin 22. Not sure what the +12VAPI is supposed to do.

The lab equipment that I am involved with normally does not have this external power supply. As a customer request, they want the normally stand alone lab equipment to send a signal to their external power supply to shut it down. My communication options to shut down the external power supply are TTL and RS232/RS485.

It seems like the simplest route will be the TTL signal. I do not have a TTL device inside of my lab equipment. The closest thing I have is a 115V control circuit and a 24VDC control circuit. My idea is integrate a separate small power supply inside of my equipment to generate the 5V I need to send the signal out on pin 22 to shut down the external power supply during an alarm condition inside my equipment. I'm not sure if this approach will work, or if there is a better way to approach it. If I have a relay controlling the 5V signal (Closed 5V open (floating) zero volts) would that work?

 

[fifty60]

sorry repeat, please see above post

 

[n1ist]

Does the TTL input have a pullup resistor? If so, a dry contact to ground would send a "0" and leaving it open a "1". If you need to source the "1", you could use a resistor and zener diode (or regulator) from the 12V rail to make 5V for a pullup resistor.
/mike

 

[gar]

140417-0856 EDT

fifty60:

Assume the TTL input is the best way to on-off control the power supply. Although you might switch the AC input power to the power supply.

There should be NO common path from the power supply 5 V common to your instrument via any cable that is to control the TTL input. This control path should be totally isolated. There should be short leads from the TTL input to where the isolation between the power supply and your instrument occurs.

I would put a 0.1 mfd 10 V disc cermanic capacitor between TTL common and the TTL input at the TTL connector, and a 100 ohm 1/4 W resistor from the TTL input to whatever is the switch that is going close to TTL common.

N1IST has suggested how to obtain a 5 V supply from the +12 V you found. When you use a different power source than Vcc for the positive logic level, then it is necessary to know its relation to the Vcc supply. I could not quickly find specs on how much + excess voltage could be applied to a gate input for a standard TTL gate.

A test with a 12 V source and a random 1N4733 5 V Zener diode produced the following voltage results across the Zener using the respective series dropping resistances:
4.4 V with 5.6 k and 1.3 mA.
4.9 V with 5.6 and 1.0 k resistors paralleled and 8.1 mA. Calculated resistance 850 ohms.
The typical minimum specified high input (minimum that a logic 1 should be) for a 74xx is 2 V, per 1976 TI TTL Data Book.

The series dropping resistor from +12 V to the Zener diode is your pullup resistor, and the Zener clamps the maximum voltage that can be applied to the gate input. The Zener cathode and series dropping resistor connect to the free end of the 100 ohm input resistor to the TTL gate. A 100 ohm resistor at the input to a standard TTL input (a 7404 gate input) when connected to common has a voltage drop of about 0.0016*100 = 0.16 V and this is sufficiently low to insure a logic 0 state.

A reed switch, low voltage drop relay, transistor, or optical coupler can be used to shunt the Zener diode for control.

.

 

[fifty60]

The problem I have are integrating zener diodes, capacitors, or resistors into my sub panel design. I generally only work with complete electronic components like relays, ssrs, contactors, and not discrete electronic components. I would probably have to build an enclosure and make it din rail mountable, and fit the discrete components onto my sub-panel that way. Any suggestions for integrating the discrete components onto the sub-panel?

 

[gar]

140417-1114 EDT

fifty60:

It is not a good idea to run TTL inputs over long open wires.

If this is a non-critical application, then just see if shorting and opening the TTL input lead to its common will accomplish your goal.

.

 

[fifty60]

So instead of using the TTL input, I may be better of adding an RS232 card to my PLC and shutting it off that way.

 

[fifty60]

Here is a link to the power supply if anyone is interested. http://www.chromaate.com/product/62000H_series_Programmable_DC_Power_Supply.htm

I'm not sure if I will be able to use the 12VDC on pin one or not. Trying to contact their tech support to no avail.

 

[fifty60]

Still trying to figure out how to do this by pretty much only looking at the manual. I do not have the power supply yet to physically try to set it up. I have a DB-25 connector on the back of the power supply. Pin 1 is a +12VDC source that I can use, with a voltage divider(600 Ohm & 500 Ohm) to set pin 22 high to start the power supply and low to shut down the power supply.

My confusion is where exactly do I install the resistors? Do I need to install them at the sub-panel of my normal equipment? Plug the DB-25 into the external power supply, and then run a pig tail back to my equipment sub panel and install the resistors in terminal blocks for my voltage divider?

Should I use the ground pin on the power supply's db-25 to set pin 22 low, or can I just open the contacts to my 5V from my voltage divider?

I attached the pinout from the manual. It does not show the pin 22 I will need to use to power off the power supply. Their tech support said that I can use Pin 1 and Pin 14 and a voltage divider to set pin 22 hi and low.

 

[GoldDigger]

It is common practice to install small components like resistors, or even active circuitry, inside a three piece connector like the DB-25 you will need to make up.
From there you can run a shielded or twisted pair wire to your dry contact relay.

Tapatalk!