T
Techy101
Hello,
First let me qualify all of this and say I am a young (professionally, not age) engineer and this is my first time designing for these types of standards. It has been and continues to be quite overwhelming but I am working my way through it. Finding this forum the other day has been wonderful and a huge source of information that helped clear up other questions I was going to be adding to this post.
I am designing a product and having difficulty understanding how to apply MOOP/MOPP rules in my circumstance. The device is table-top, stand-alone, and powered by 4x NiMH rechargeable batteries. They are charged outside of the device and the device itself it has no possible connection to mains and it has no electrical connection to any other devices. The device is an iontophoretic stimulator which delivers a drug to a patient via a constant current and has four galvanically isolated outputs for delivering to four sites simultaneously, each site with its own return electrode. The positive electrode itself sits at the top of a capsule which is then filled with a solution of the desired drug. The electrode itself doesn’t actually contact the patient skin, the connection is made through the solution. (Section 8.7.4.7 (f) would apply). It is for use in a doctor’s office environment only and is, more or less, an accessory to a larger device we sell.
As I said, the device is powered by four NiMH batteries in series. The batteries supply the MCU and UI system as well as a pair of load switches, controlled by the MCU, which enable battery power to four flyback converters when a treatment has been initiated. These flybacks are used to step the voltage up to 120VDC, supplying a low-side constant current source for patient stimulation.
My confusion lies in the fact that this type of system doesn’t seem to be well defined in section 8 of 60601-1 and my questions are:
1.
Section 8.4.1 states that “The limits specified in 8.4.2 do not apply to currents that are intended to flow through the body of the PATIENT to produce a physiological effect during NORMAL USE.”
Annex A Subclause 8.4.1 also states: “This standard does not specify any limits for currents that are intended to produce a physiological effect in the patient, but particular standards can do so. Any other currents flowing between PATIENT CONNECTIONS are subject to the specified limits for PATIENT AUXILIARY CURRENT.”
This obviously describes my device. My interpretation of this would be that while my device is actively delivering current to a patient the currents are not measured, but when it is sitting in standby they would be.
2.
Section 8.5.3 states “for other INTERNALLY POWERED ME EQUIPMENT, the MAXIMUM MAINS VOLTAGE is 250 V.”
3.
3.110 defines a SECONDARY CIRCUIT as “circuit which is separated from the MAINS PART by at least one MEANS OF PROTECTION and derives its power from a transformer, converter or equivalent isolation device, or from an INTERNAL ELECTRICAL POWER SOURCE”
Section 8.2.1.12 states that “Where the SECONDARY CIRCUIT is earthed or the ME EQUIPMENT is INTERNALLY POWERED, Table 15 applies.” As well as “The column for circuits not subject to transient overvoltages applies to … circuits in INTERNALLY POWERED ME EQUIPMENT.”
I know this is a lot of questions packed in, but I tried to break them out in a readable/logical manner. Ultimately I am just trying to figure out what creepage and clearance values I need to use and what (if any) leakage currents I need to be concerned with for safety testing.
Thank you very much,
Matthew
First let me qualify all of this and say I am a young (professionally, not age) engineer and this is my first time designing for these types of standards. It has been and continues to be quite overwhelming but I am working my way through it. Finding this forum the other day has been wonderful and a huge source of information that helped clear up other questions I was going to be adding to this post.
I am designing a product and having difficulty understanding how to apply MOOP/MOPP rules in my circumstance. The device is table-top, stand-alone, and powered by 4x NiMH rechargeable batteries. They are charged outside of the device and the device itself it has no possible connection to mains and it has no electrical connection to any other devices. The device is an iontophoretic stimulator which delivers a drug to a patient via a constant current and has four galvanically isolated outputs for delivering to four sites simultaneously, each site with its own return electrode. The positive electrode itself sits at the top of a capsule which is then filled with a solution of the desired drug. The electrode itself doesn’t actually contact the patient skin, the connection is made through the solution. (Section 8.7.4.7 (f) would apply). It is for use in a doctor’s office environment only and is, more or less, an accessory to a larger device we sell.
As I said, the device is powered by four NiMH batteries in series. The batteries supply the MCU and UI system as well as a pair of load switches, controlled by the MCU, which enable battery power to four flyback converters when a treatment has been initiated. These flybacks are used to step the voltage up to 120VDC, supplying a low-side constant current source for patient stimulation.
My confusion lies in the fact that this type of system doesn’t seem to be well defined in section 8 of 60601-1 and my questions are:
1.
Section 8.4.1 states that “The limits specified in 8.4.2 do not apply to currents that are intended to flow through the body of the PATIENT to produce a physiological effect during NORMAL USE.”
Annex A Subclause 8.4.1 also states: “This standard does not specify any limits for currents that are intended to produce a physiological effect in the patient, but particular standards can do so. Any other currents flowing between PATIENT CONNECTIONS are subject to the specified limits for PATIENT AUXILIARY CURRENT.”
This obviously describes my device. My interpretation of this would be that while my device is actively delivering current to a patient the currents are not measured, but when it is sitting in standby they would be.
- Would this measurement apply to my type of device?
- If so, would it require checking for currents between, say, channel 1-positive and channel 3-return, etc…?
2.
Section 8.5.3 states “for other INTERNALLY POWERED ME EQUIPMENT, the MAXIMUM MAINS VOLTAGE is 250 V.”
- Does this mean that I need to have 4mm clearances around the PCB traces coming from the battery per Table 13? Looking at Annex A Subclause 8.5.3 didn’t seem to help clear this up and 4mm seems rather absurd.
3.
3.110 defines a SECONDARY CIRCUIT as “circuit which is separated from the MAINS PART by at least one MEANS OF PROTECTION and derives its power from a transformer, converter or equivalent isolation device, or from an INTERNAL ELECTRICAL POWER SOURCE”
Section 8.2.1.12 states that “Where the SECONDARY CIRCUIT is earthed or the ME EQUIPMENT is INTERNALLY POWERED, Table 15 applies.” As well as “The column for circuits not subject to transient overvoltages applies to … circuits in INTERNALLY POWERED ME EQUIPMENT.”
- Based on these I understand my device to be already considered a secondary circuit, so would this count as one MOP on its own?
- Table 15 only covers MOOP not MOPP. Because this device is connected to a patient it seems like MOPP would be what I was concerned with but, per 8.2.1.12, I’m looking at table 15 and thus MOOP. Am I correct that Table 15 is where I need to get my clearance values from?
- When dealing with the traces on my PCB that are at 120VDC, I interpret this to be the WORKING VOLTAGE. Per Table 15 I would need 0.7mm clearance for one MOOP and 1.4mm clearance for two MOOP. Because my device is already a secondary circuit can I get away with only using the 0.7mm One MOOP or do I still need to do the 1.4mm Two MOOP?
- Finally, Table 16 says it applies to all situations, but that would say that I need 3mm creepage distance to have two MOOP. Does this table apply?
I know this is a lot of questions packed in, but I tried to break them out in a readable/logical manner. Ultimately I am just trying to figure out what creepage and clearance values I need to use and what (if any) leakage currents I need to be concerned with for safety testing.
Thank you very much,
Matthew