Connecting Simpson 150-2 Amp Clamp to a DSO - Page 1
Forum section: electronics / testgear

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 17, 2015, 09:53:42 pm
content: Found this today in thrift store, seemed like a reasonable deal, so I bought it. It came with the operator's manual, registration card and original box. I am guessing this is a mid-1980s product. The manual mentions connecting it to 250, 255, 260XL, 261, 270, 260 series 8 or 270 series 5 testers. I have an inoperative 260P somewhere, so maybe this is a good time to resurrect it.Meanwhile, the thought crossed my mind, that this might be an interesting probe to connect to a DSO, such that it might allow me to visually see motor start-up current spike, followed by normal run current. the manual says that it should be connected to a device with a 2.5 volt AC, or 3 volt AC scale, and that the device should have a sensitivity of 5000 ohm per volt AC. A DSO has a considerably higher input impedance than that (1M or 10M). To present the proper load to the clamp, should I put a resistor across the input connection ? If so, it sounds like 12.5K or 15K resistor.Will this even work ?

author: Seekonk
author_rank: Super Contributor
timestamp: February 17, 2015, 10:12:37 pm
content: Since it has a current range switch, I believe it is already terminated inside and that 5000ohms/volt is the minimum it can be connected to. An ohms check should verify that. It should be fairly low, less than 200. If it jumps up dramatically on the most sensitive range, a 15K might be appropriate. There is always the lightbulb test. Multiple loops can simulate high currents.

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 17, 2015, 10:34:12 pm
content: Quote from: Seekonk on February 17, 2015, 10:12:37 pmThe most sensitive range is showing 505 ohms, the next range up (approximately twice the current) reads 464. Each higher range shows a lower resistance, until the highest current range is 237 ohms.

author: Seekonk
author_rank: Super Contributor
timestamp: February 18, 2015, 11:37:26 am
content: With or without a load it would only vary 3%. That could be within the accuracy of the clamp, dust or rust on mating surfaces could change it that much. Only a test would determine if adding a load improves accuracy.

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 23, 2015, 04:08:25 am
content: This evening I was able to restore my Simpson 260-6P to functional condition. Now I need to make a cable to connect to it to the amp clamp. The banana plugs for the 260 are easy enough, but the pins on the amp clamp (3rd photo) are somewhat unique. Anyone know what those might be called, or where to order a matching plug from ?

author: tautech
author_rank: Super Contributor
timestamp: February 23, 2015, 10:25:35 am
content: Quote from: cosmicray on February 23, 2015, 04:08:25 amI'd be surprised if the correct plug can be found and as your OP stated for DSO connection you'd want to use a Coax cable.Does the clamp have a frequency rating, it might be only 50 or 60 Hz rated and therefore barely of any use for a DSO.

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 23, 2015, 01:58:34 pm
content: Quote from: tautech on February 23, 2015, 10:25:35 amThe manual says 60 Hz, but that it can be recalibrated for 50 Hz or other frequencies. It also mentions that the output voltage is protected (clamped I would presume) at 6.5V, so that putting it on the wrong scale will not produce a lethal voltage at the pins. That explains how they can get away with having male pins on a device that produces voltage.Regardless of DSO or 260, I sill need to ID that connector. It lookssomewhatsimilar to a standard non-polarized AC mains jack that is on the back on many double insulated devices. Tried one of those cables last night, but the cable shroud was a mm or two larger than the opening, and the pins on the amp clamp are larger than the female pins on the cable. The proper cable (to connect to a 260) may be available, but the price it is listed for is rather high. Most places that list the proper part number have a disclaimer concerning availability. I'm less inclined to chase down that cable.

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 23, 2015, 04:13:16 pm
content: As best as I can measure, the pins are 3mm diameter with 7mm (or 1/4 inch) pitch. They are two pins on a small piece of insulating board. I'm trying to find out what is the mating plug for that.

author: SeanB
author_rank: Super Contributor
timestamp: February 23, 2015, 04:40:36 pm
content: Phillips shaver plug looks like a likely candidate for the cordset.

author: cosmicray
author_rank: Frequent Contributor
timestamp: February 23, 2015, 05:26:21 pm
content: It just occurred to me that the pins look similar to the larger variety vacuum tube pins (not smaller wire like ones). I'm thinking of the vacuum tube pins that were part of a phenolic/bakelite base. The small tubes had wire-like pins came straight out of the glass tube. wiki says that the pin thickness on an octal tube was 2.36mm, and several other tube types were closer to 3mm. Might be coincidence, but the resemblance is striking.