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HP Forum Archive 13

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Hearing HP-IL
Message #1 Posted by Renato on 21 May 2003, 11:17 p.m.

I got a 3421a unit. Nice one - three 10ch cards. As the sealed lead acid battery is bad, i decided to try reviving it. First approach is to let the 3421a try to recharge the battery, while monitoring voltage using the front panel inputs.

The point is: using the DCV routine, the 41cv is monitoring voltage on the battery continuously - late at night (youd guessed it...) I am certain that i can hear HP-IL module humming, in sync with the voltage readings. My guess is that HP-IL is using serial communications at around 2KHz. Does anynone know about it ? If Im right, im not taking my ears to calibration :^)

Also, NiCd battery replacement is a popular subject here. What about SLA batteries replacement ? The 3421a uses a 3.2 AH 6V Panasonic. I found a Powersonic equivalent, at US$15.00. See http://www.power-sonic.com/, model is PS632. If anyone knows another alternative, please let me know.

      
Re: Hearing HP-IL
Message #2 Posted by Vieira, Luiz C. (Brazil) on 22 May 2003, 12:05 a.m.,
in response to message #1 by Renato

Hi, Renato (lucky one!).

Congratulations! You have a nice data acquisiton system!

Just one information: the HPIL is electrically (de)coupled by a set of three independant toroid-core transformes built as one single unit with many terminals. You bet you're hearing them.

Keep them fine!

Luiz C. Vieira - Brazil

      
Re: Hearing HP-IL
Message #3 Posted by Christoph Klug on 22 May 2003, 1:53 p.m.,
in response to message #1 by Renato

Dear Renato,

the HP3421 IL-Data Logger is a nice HP-IL device. From a German supplier for model cars I get a replacement battery which is compatible to the original battery. Same batteries are used in the IL-Disk drive and the HP3468 IL-Digital Multimeter.

When you replace the battery do not remove the internal option cards than you need a new calibration of the system. Replacing the battery is possible with special screw drivers and tools.

Last not least for advanced data logging and measurement applications also I/O-Board and IL2000 System exist. This includes some nice features like, much digital input/output lines, some analogue input/output lines with 12bit resolution, some different voltage supply lines, a modular hardware desing, solar charger option, control software for HP41. If you want to realise a data logger application which is limited by the features of the HP3421 than take the I/O-Board or IL2000 system. For more details refer to HP-Museum article forum :

003 HP41 Hardware Interfacing Activities
192 Interfacing IL2000 System to Analogue World
311 HP41-PC Gateway & Emulator

Best wishes from Germany - Christoph Klug

            
Re: Hearing HP-IL
Message #4 Posted by kim on 22 May 2003, 5:17 p.m.,
in response to message #3 by Christoph Klug

Hr Klug

I live in Stuttgart (you guessed right I'm not German).

Could you possible help directing me to the model car 'dealership'?

Kim

PS.: I own one of you IL IF's. Have not tried to connect it yet. But once I get the time (probably in fall) I'll try it out in the dock of my OmniBook 800CT...

                  
Re: Hearing HP-IL
Message #5 Posted by Massimo Gnerucci (Italy) on 23 May 2003, 2:50 a.m.,
in response to message #4 by kim

PS.: I own one of you IL IF's. Have not tried to connect it yet. But once I get the time (probably in fall) I'll try it out in the dock of my OmniBook 800CT...

You'll find it working nicely in your OB800CT... at least, mine does.

Enjoy,
Massimo

                        
Was: Hearing HP-IL Now: Help with IL Card for OB800CT
Message #6 Posted by kim on 25 May 2003, 3:49 p.m.,
in response to message #5 by Massimo Gnerucci (Italy)

I got to play with my 'Klug' IL IF for the PC (OB800CT). I was planning for fall and today looked a lot like fall so of I went on and tried it out.

It went reasonably well I got the test to tell me that Card was found, loop was OK, and ocassionally it found stuff on the loop, most succesfull with 71B in 'control off' mode.

Using the Monitor i found that some commands turn up twice so my conclusion is that my OB800CT is to fast :')

I have tried the Ctrl+Alt+Minus but it does do it.

Does anybody have an idea?

Kim

                              
Re: Help with IL Card for OB800CT
Message #7 Posted by Christoph Klug on 26 May 2003, 4:49 a.m.,
in response to message #6 by kim

Dear Massimo,

I want to help you with your HP-IL/PC installation. Please give me informations about your operating system and the software like Link Plus, or TRANS41 or EMU41 ?

Best wishes from Germany - Christoph Klug

            
Re: Hearing HP-IL
Message #8 Posted by Renato on 23 May 2003, 12:52 a.m.,
in response to message #3 by Christoph Klug

Dear Christof,

Thank you for the information. Do you know the brand and model# for the replacement battery you found ? Maybe I can find it here in Brazil . This would me much more convenient than the US source I found.

I did remove one internal option card, to remove the battery. I did not disconnect any cables for that - I guess recalibration will not be necessary . Do you agree ?

Thank you for the articles refs. Ill look at them. I got this 3421a just for fun - I mean, I dont have a specific application for it. Looks like other HP-IL itens might bring more fun ...

Best regards from Brazil,

Renato

                  
Replacement battery for HP3421
Message #9 Posted by Christoph Klug on 23 May 2003, 2:54 a.m.,
in response to message #8 by Renato

Dear HP3421 enthusiasts,

yes the IL-Datalogger is a nice unit - also EMU41 with HP-Il/PC Interface Card have the power to control the HP3421.

For ordering a replacement battery refer to www.batt-mann.de In the list of the shop you will find :

Blei Akkus - 6V / 2,4Ah / 66 x 33 x 99mm

The identical battery is used by the IL-Disk Drive. About this you find some messages in the HP-Museum forum. When I remember correctly Raimund del Torno created a message about an alternative battery supplier in Hamburg...

Best wishes from Germany, and now realise your interfacing applications "to the world" (Gary Friedman) - or "to the future" (my own idea) - Christoph Klug

                        
Re: Replacement battery for HP3421
Message #10 Posted by Ellis Easley on 23 May 2003, 6:19 a.m.,
in response to message #9 by Christoph Klug

The 3421 came with a slightly larger battery, 3.2 A-H. The replacement that a local battery store found for me (exact fit as original Panasonic battery) is "Power Patrol SLA0895", 6V 3.8 A-H.

                  
Found a replacement battery for 3421a
Message #11 Posted by Renato on 24 May 2003, 2:18 p.m.,
in response to message #8 by Renato

I just bought a Unipower 6V 2.8AH SLA battery. It is shorter than the original panasonic, but H and W are the same - it fits perfectly in the 3421a. Paid around us$9.00

      
self-monitoring battery
Message #12 Posted by Ellis Easley on 23 May 2003, 9:26 a.m.,
in response to message #1 by Renato

Did you connect the low input to the battery negative terminal? If so, you have shorted out the battery fuse with your test lead! The fuse is between the battery negative terminal and ground. There is also a diode connected with its cathode to the battery positive terminal and anode to ground, between this diode and the fuse, if you accidentally connect the battery backward, the diode will conduct and the fuse will open, protecting the system.

In general, it is not a good idea to measure anything in a test instrument with itself unless it was designed to do so for test purposes. In this case, it would probably be acceptable to measure the battery voltage by connecting just the high input to the battery positive terminal, with a small error due to the voltage drop of the fuse. You would fail to sense an open fuse, but that is impossible anyway because the negative terminal of the battery charging circuit is connected to ground which is ultimately connected to the "analog ground" which the low input is connected to. I haven't yet determined from the service manual just where the analog and digital grounds are joined but I'm pretty sure they are connected, at just one specific point to avoid ground loops affecting the accuracy of the readings. These grounds are not connected to the power cord ground, there is only a spark gap between them.

With your mux board, you could measure the positive terminal and the negative terminal of the battery (with just the high inputs) and accomplish two things: (1)correct the reading from the positive terminal by subtracting the voltage on the negative terminal, which is the voltage drop of the fuse and the wire and (2) detect an open fuse, which would show up as a unusually high voltage on the negative terminal: even if the battery is fully charged and measures over 6V without any charging current, the positive battery terminal will be driven to 7.2V by the charging circuit so you would measure up to 1.2V on the negative battery terminal if the fuse was open.

Another measurement you can make regarding the battery charging circuit is the voltage across the current sense resistor, R705, a 0.27 ohm resistor located between the power transistor Q700 and the power transformer T700. One end is connected to ground and the other end is connected to the negative terminal of the bridge rectifier and its filter capacitor, C700. The negative lead of C700 is a good place to connect to it but it is hard to reach if you have the HPIB board installed, the resistor is easy to reach. I have been using my 3421A to charge some different size 6V lead-acid batteries and so I am very familiar with this circuit right now! After you let the battery run the system for a few minutes (my unit draws about 200 mA - this doesn't show up at the current sense resistor if you disconnect the AC and just let the battery power the unit), if you then turn the unit off and connect the AC again, the charging current goes to the limit right away (on my unit), I measure -136 mV on R705 which is about 1/2 Amp. While the current limit circuit is operating, the voltage is not being regulated (they work through the same pass transistor). After a while the current starts dropping from the limit value and at this point the voltage regulator circuit starts working. My unit puts about 7.2 V on the battery at room temperature (there is an NTC thermister in the voltage regulator circuit that reduces the voltage as the temperature inside the cabinet rises). If you have one of the Panasonic batteries, it should have a description of the charging specifications printed on it. Mine says "Constant voltage charge - Cycle use: 7.25~7.45V (25 deg. C) - (Initial current: less than 1.28A [always .4 times the A-H rating on different size batteries] - Standby use: 6.8~6.9V (25 deg. C)" I have some different size Panasonic batteries that have slightly different voltages printed on them (10 A-H: says 7.3~7.5V for Cycle use). It appears that HP has chosen a voltage between the Cycle and Standby ranges. The different batteries that I have measured finally settle to a charging current corresponding to about 4 to 10 mV across the current sense resistor (about 15 to 40 mA).

With all my oscilloscopes, I need to connect one to this charging circuit so I can understand the function of one component: a capacitor connected to the outputs of the voltage regulator and current limit comparators. There is an LM393 dual comparator with open collector outputs doing both jobs. The voltage regulator comparator drives its output low when the battery voltage rises above its limit. The current limit comparator drives its output low when the current rises over its limit. The two outputs are "wire-ORed" together. At the outputs there is a 33.2K pullup resistor to the unregulated supply (12-18V) and a 1 microfarad capacitor to ground and the base of an NPN transistor with its emitter going to ground through a 200 ohm resistor (feedback, current limit?). The collector of the NPN goes to the base of a PNP power transistor whose emitter goes to the unregulated supply and collector to the positive battery terminal through a forward biased diode (I think this diode is to keep the charging circuit from draining the battery when the AC is disconnected). So the NPN is a phase inverter and voltage level shifter for the PNP pass transistor. When a rising voltage on the base of the NPN turns it on, it drops the voltage on the base of the PNP and turns it on. As long as either comparator output is low (voltage or current too high), the transistors are off. When both comparator outputs are high (voltage and current below their limits), the 33.2K pullup resistor starts charging the 1 microfarad capacitor. If the unregulated supply is at 18V, the 33.2K resistor would source .54 mA which would take a little over 1 ms to charge the 1 microfarad capacitor to 0.6V, at which point the NPN would begin to turn on. The capacitor would continue to charge, shunting some of the current that would otherwise turn the transistor on more quickly. This is where the feedback from the 200 ohm emitter resistor comes in, because as the NPN collector current (= PNP base current) rises, so does the NPN emitter current and emitter voltage and base voltage, which allows the capacitor to keep charging. If the NPN emitter was grounded and the 200 ohm resistor was between the NPN collector and PNP base, providing current limiting, the NPN base voltage wouldn't rise much after the transistor started to turn on, so the capacitor wouldn't charge much more and the transistor would turn on more quickly. When either comparator output goes low again (current or voltage rising above limit), its open collector output transistor turns on and shorts the capacitor to ground, quickly discharging it and turning off the NPN transistor and the PNP pass transistor. Now the 200 ohm emitter resistor might make the NPN turn off more quickly, because its voltage drop raises the emitter voltage and causes the base voltage required to keep the transistor turned on to be higher. Drawing a comparison to a music synthesizer, the capacitor (and the 200 ohm emitter resistor?) cause the battery charging current to have a slow attack and a fast decay. I suspect the voltage at the comparator outputs is a sawtooth wave.

Maybe the capacitor is there to slow the circuit down and prevent uncontrolled oscillations that might occur due to the lack of hysteresis in the comparator circuits. IIRC, the 9114 battery charging circuit has a comparator with hysteresis to turn on a sensitive gate SCR (gate driven with DC, load driven with pulsating [unfiltered] DC). You can see the comparator limits by monitoring the battery voltage and watching the LED (which provides a trickle charge current when the SCR is off).

            
Re: self-monitoring battery
Message #13 Posted by Renato on 23 May 2003, 10:57 a.m.,
in response to message #12 by Ellis Easley

Ellis,

Thank you for so much information.

You said: "Did you connect the low input to the battery negative terminal? If so, you have shorted out the battery fuse with your test lead!" My comments: I did connect low input on ch 0 to battery negative. Consequence is that when when a measurement is started on ch 0, 3421a locks up, and needs off/on cycle. There seems to be no further consequences (I hope...).

Connecting battery terminals to front panel input seems to be ok - DCV readings are consistent. Do you know if there is any risk from doing this ?

                  
Re: self-monitoring battery
Message #14 Posted by Ellis Easley on 24 May 2003, 5:21 a.m.,
in response to message #13 by Renato

Only a possible ground loop. Bypassing the fuse is a potential safety (at least to the machine) issue but other than causing a ground loop I don't think it would affect the reading. I'm surprised that connecting to the negative terminal through the mux causes a problem! Unless it is that when the relay on the mux closes, it causes a transient on ground that leads to a CMOS chip latching up. I verified that analog ground (for instance, the low input on the front panel) does go back to power supply ground (like the fuse on the battery negative terminal) but if you track it down in the PCB traces, I think you will find that there is exactly one point where the analog ground connections join the power supply, or digital, ground. Adding another wire from the battery negative terminal to the low input creates the ground loop that can cause problems.

I've been thinking some more about the 1 microfarad capacitor and the 200 ohm resistor in the charging circuit. Now I think that the capacitor's main job is to integrate the pulses on the comparator outputs and the reason for the feedback from the 200 ohm resistor is to do a voltage to current conversion from the capacitor voltage to the NPN transistor collector current. So the comparators are generating a pulse width modulated error voltage reflecting the battery's voltage as compared to a reference, which the capacitor integrates to an analog voltage level, and then the NPN transistor and the 200 ohm resistor convert the capacitor voltage to a current to drive the PNP base, thereby controlling the voltage at the battery.

                        
Re: self-monitoring battery
Message #15 Posted by Renato on 24 May 2003, 2:29 p.m.,
in response to message #14 by Ellis Easley

Ellis, Although I dont fully understand your explanations, I agree that connecting ch0 low input to battey negative does not cause harm. About locking the 3421a, maybe this unit is not perfect - I just got it, and do not have a assesment about its condition.

Thank you.

Renato

                              
Re: self-monitoring battery
Message #16 Posted by Ellis Easley on 25 May 2003, 2:48 a.m.,
in response to message #15 by Renato

I don't expect it will cause harm to the machine but I still believe it can cause erroneous operation because of a ground loop. Also, although you are using an instrument to measure inside itself which is really not a good idea, since the battery negative terminal is in fact connected (through the fuse) to the digital ground and to the analog ground and the low input, you don't need to connect it with another wire to measure the voltage at the battery positive terminal. If fact, if you want to measure the voltage between any two points in the 3421A with itself it would be best to measure the voltage on each point separately using only one wire to the high input and then calculate the difference between the two readings. And there are plenty of points in the analog input section that it would be a very bad idea to connect to the high input.

The thing about the ground loop is that inside the 3421A HP has gone to pains to make sure everything connected to the low input of the sensitive input circuit is isolated from the electrically noisy ground of the logic circuits and power supply. By running a wire from the battery negative terminal to the low input, you are defeating HP's isolation efforts and exposing the input circuitry to all that noise. It's completely different from connecting the low input to a noisy ground on another piece of equipment because the 3421A is designed to only measure the difference in voltage between the low and high inputs and ignore the "common mode" voltage upon which is riding every signal in the equipment under test. The manual has a description of how the instrument even works to average out the differential mode noise (originating in the AC power mains) that comes in on a signal to be measured, which is the reason for the 50/60 Hz switch on the back panel.

Here's an example of what can go wrong: I have some HP equipment that have voltage regulators with pass transistors in the negative side of the supply - not negative voltage supplies but positive voltage supplies which are regulated by having pass transistors between the negative side of the unregulated supply and ground. The positive output comes directly from the positive side of the unregulated supply. The 3421A has something a little like this in that it has the 0.27 ohm current sense resistor between the negative side of the bridge rectifier and ground. The significance is that there is a point (in an otherwise positive-voltage-with-respect-to-ground circuit) more negative than ground. If the 3421A had such a negative side voltage regulator, with a pass transistor between the negative battery terminal and ground, and you connected the low input to the battery negative terminal, you would short out the pass transistor and all the circuits in the unit would be exposed to a higher voltage than they were supposed to see.

                                    
Re: self-monitoring battery
Message #17 Posted by Renato on 27 May 2003, 1:50 a.m.,
in response to message #16 by Ellis Easley

Ouch. I guess I was pretty lucky.

Thanks for the information. BTW: is your 3421 being useful ? What for ?

Renato

                                          
Re: self-monitoring battery
Message #18 Posted by Ellis Easley on 28 May 2003, 7:28 p.m.,
in response to message #17 by Renato

Currently it is just charging batteries! (or should I say "constant voltagely"?) Actually, one of the projects I have in mind for it is to test batteries - discharge, recharge, monitor voltage and current, calculate capacity, etc. - just for self-edification.

                                                
Re: self-monitoring battery
Message #19 Posted by Renato on 28 May 2003, 10:01 p.m.,
in response to message #18 by Ellis Easley

Ellis, Quite interesting ! I could have written your exact words. Battery charging was a important issue for me in the 80s. It is important again now - my woodstock collection is almost complete, and if I succeed on efficiently handling batteries, i will try to use a 21 daily.

Best regards from Brazil.

Renato


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